I have a decent size room 20’x33’x9’.  Due to the placement of some large columns I need to place my equipment on the long wall.  While I can achieve an equilateral triangle between seat and speakers (11’ on all sides) .... I am unable to have the front of the speakers more than 3’ from the front wall.  I am using Avantgarde Uno speakers with Pass Labs XA 60.8 amp and AR Ref 6 pre.  Sources are Lumin X1 and SME 20.  The overall sound and imaging are wonderful.  There are two problems that I can’t seem to get right.  First, the soundstage is rather narrow ... does extend beyond the speakers (have tried every off to on axis position).  Second, the image is detailed/precise but not deep ... it just sort of hangs on the wall 3’ behind the face of the speakers.  I believe that the problems are due the speakers not being far enough from the front wall but I can’t move them out more (due to the columns I mention).  Any suggestions on how I might fix these two problems?
While reading this thread I began to wonder about the carpet on the wall behind the speakers. I put it there when the projection setup was installed, but there are other ways to darken the wall. Is that counter productive? The speakers are a pair of KEF Reference 1s supplement below 80 Hz by a pair of Velodyne HGS-15 with acoustic bass management. The equipment that used to be on an adjacent wall now resides in a low (20") rack between the KEFs. In the past I’ve avoided placing anything between the speakers, but the low rack between them makes for a neat setup. If I did move the rack, I’d leave the amp on the floor between the speakers so there would be only a pair of balanced cables running from the preamp to the amp.
Don't know where this equilateral triangle deal came from but it is erroneous.  

Speaker setup is a two-step process. 

Step one, move them around relative to the walls listening for bass balance and tone. Listener position matters as much as speaker location so listen to each speaker location from closer and further away. Step One the speakers do not need to be perfectly equidistant or symmetrical, but pretty close. 

Step Two, now from the smoothest sounding location measure very accurately to get them perfectly equidistant and symmetrical. Listen for image focus and sound stage width and depth. Adjust the toe in very slightly and the image focus and depth will be greater. Adjust the toe out very slightly and the sound stage width will expand. Equidistance and symmetry must be precise each and every time or you will lose image focus and think it was due to changing toe when really it was sloppy symmetry. 

When you are happy with the balance you are done. Does not matter what the distances are. That is all simplified to the point of rubbish. This is how you do it. 
Very cool speakers,
after years of trying the equilateral triangle at 8 feet 
and trying to extend the 8 feet feet listener to my rooms max of 8 ft 6 in
I tried something different .
My speakers manual suggested 8 feet apart and 8 to 10 feet from the listener , so what's the difference ?  
The angle from the listener to the speakers ,
from 60 degrees to 47.2 so if you haven't already maybe try
moving your speakers to 8 ft 10 in  apart with your 11 feet to the listener
you'll have an angle of 47.2 degrees .
Just a thought and maybe worth a try .

I have had different models of Audio Physic speakers. They all produced a wide soundstage beyond the speaker boundaries. I have tried many positions in a few very different rooms. The speakers just disappeared in a very wide stage. Most were older models though, when the original designer Joaquin Gerhard was still with the company. (Designer spelling may be incorrect.)
Interesting post Duke. Because some of the most enthusiastic comments on my system have to do with superb image focus and a stage that extends beyond the speakers. My feeling for some time now has been more you are there than they are here. My room, in other words, disappears. The untreated (well, HFT) side walls do not seem to interfere with rock solid imaging. Each record is not only a different sound, it is a different world. Some you are right in it, others it is further away, some it is rather flat, still others it extends deep and wide.

This is actually one of the hardest things to get across to people, because there is a tendency to assume what you are hearing is the system. The more that is the case the easier it is to evaluate. But the more the system disappears the harder this becomes. Depending on what I play you could leave convinced my system is flat and narrow, or deep and wide, but only a great deal of time listening to a wide range of music will reveal the truth, that it was the recordings not the system.  

I suspect this is because as important as the speakers and the room are, still they are but two on a very long list of things that matter.
Thanks Duke. If I’m understanding correctly you are describing the kind of sound that I really like (with the early sidewall relections). Found in bipoles (e.g. my ancient Mirage M3s), wide dispersion bookshelf speakers (my LSA bookshelf) and I would guess omnidirectionals. The speakers disappear, and you can walk around the room and the speakers remain disappeared.  Not a goal, just a description of a kind of sound I like.
Duke is right and I set up my system in a similar way with essentially no early reflections. This results in a more focused, palpable image. Whether you are "here" or "there" IMHO depends on the recording. A good live concert recording will put you "there" assuming your room acoustics are controlled. Studio recordings are a toss up and frequently very confused with various instruments and voices in entirely different environments. Overdubs can be very weird then the engineer adds some reverb to the voice and puts it over in the next county. I like it when the instruments seem as if they are in the same room together an effect that seems to be difficult for engineers to achieve. I really like a good studio recording but I admit the recordings I like the most are live. DTD records are wonderful for this very reason. 
A few thoughts:

A deep, layered soundstage is fairly difficult to achieve IME. Choose a couple recordings to use as a reference that will give you a basis for judging your progress. "Coal Train" (Hugh Masekela - Hope album) and "Roughest Place in Town" (Stevie Ray Vaughn - Couldn't Stand the Weather) are good audio show favorites that have a lot of depth in the right system. If you are into Classical music then Massenet (City of Birmingham Orchestra, Klavier Records) is almost eerie on the right system. I have a pair of Thiel CS6 speakers driven by a Krell KRC-2 and KSA 300S. I have a big room and lots of flexibility of placement. The speakers are about 5 feet from the front wall and 4 to 5 feet from the side walls and about 9' apart.

Speaking of audio shows, they are coming back this year and going to a show is an excellent way to calibrate your ears and figure out where your system sits in the scheme of things. At the shows I've been to I have heard excellent soundstage depth on only a few systems. Most have excellent articulation in the left/right dimension but most do not really allow you to see deeply into the soundstage.

There are several pieces of gear that do what you are seeking. Carver made a "Sonic Holography" C9 processor (I have one) that adds depth but you have to sit right in the sweet spot to get the effect. You might have to be patient to find one but they are not very expensive on the used market.

A company called BSG made a processor with the model designation of QOL that also performs this function (I have one of these too). I like this processor better because it is more forgiving about exactly where you are sitting and the effect is a little more subtle than the Carver. These are more rare than the Carver but if you patient you can find one for under a grand.

The other option I know of is the Atmosphere by Synergistic Research. I heard one of these at AXPONA and it was pretty amazing on a large pair of Magicos. I'm looking forward to hearing one of these again.

I got a nice confirmation about my system when an audio buddy visited for a few days recently. He is the guy who sold me the Thiel speakers. He was very impressed with the way my system sounded and particularly commented about the soundstage depth. He could readily hear the positive difference from the QOL processor. He told me that he had never heard the Thiels sound that good in his system.

A soundstage which routinely "extends beyond the speakers" is a characteristic often found with wide-pattern loudspeakers in situations which result in strong early same-side-wall reflections. These reflections broaden the apparent source width (ASW), according to Floyd Toole, and are considered to be desirable by most listeners (and undesirable by some). Their downside is that they also degrade image precision and can cause coloration (according to Geddes), can degrade clarity (Griesinger), and can contribute to "small room signature", which is the imposition of your room’s acoustic signature atop the venue signature on the recording. (Note that recordings which are deliberately intended to image beyond the speakers, such as the aforementioned "Amused to Death", DO NOT rely on strong early sidewall reflections.)

Chili42 I expect that your wide room’s inherent lack of early sidewall reflections is why you aren’t experiencing the wide soundstage that you expected. I’m among the (apparent) minority who prefers the attributes which accrue to freedom from those early sidewall reflections.

In particular, if we can solve the frontwall (and possible back wall) early reflection issues, you MIGHT end up with a system where the acoustic signature on the recording tends to dominate over the acoustic signature of your room. Ime this is quite enjoyable, and can result in a "you are there" experience which varies significantly from one recording to the next, instead of a "they are here" experience whose spatial qualities are dominated by the playback room.

Imo, ime, ymmv, etc.

Have you tried putting nothing, zero, zilch between the speakers? That made a huge difference for me with my speakers 30" from the front wall. I had my tweeters 45" from the side walls. Huge soundstage side to side and top to bottom. Depth of soundstage was pretty good...but I've heard better (speakers were 12' from the front wall).
If you can you might want to try the off axis set up. This is what is used by a lot of people at shows. Start in a corner of the room then place one speaker wide and the other more forward. There was a thread on this set up here but i do not have to locate for you. Here is another link.
Duke has it right. I assume neither speaker is in a corner? If neither speaker is in a corner then you have six early reflections to worry about, two between the speakers, two on the ceiling and two on the floor. The two between the speaker are the ones to worry about first. Moving the speakers just shifts the early reflections a little and delays their timing a little. If you treat them correctly moving the speaker does not matter! You can actually put them closer to the wall. The mirror method Duke describes is the way to find them. Sit in the listening position and have a helper hold a mirror against the front wall at ear level and have them slowly move it until you can see the speaker in the mirror. Mark that point. Then do it for the other side. Get 4" acoustic tile from here   They are dirt cheap and allow you to experiment. If you want something more fancy looking you can get that later once you know what you are doing. Place 4 tiles at ear height centered on the early reflection points arranged in a big square 2 X 2 feet. Then have a listen. You can do the ceiling if you like. On the floor use a rug or carpet. Try making the squares bigger  3 X 3 feet and see what it sounds like. You will change the frequency response of what you are hearing a bit dropping the high frequency content.  A pro will measure it with a microphone and if needed make corrections by digital EQ. Unlike analog EQ, digital EQ will not add distortion or phase issues. Other than the frequency response changes it is invisible. 
Personally, I do not think you can overdo it. Adding more absorption does seem to make the system seem more dull but in my experience if you want the sensation of having instruments hanging in space, like you can reach out and touch them you need to severely limit reflections. Those of us in the know use speakers with very limited dispersion and kill the early reflections as much as possible. People will initially think these systems sound lifeless until they sit and listen to them a bit and realize that no frequencies are missing and the image is spectacular. The room has disappeared. For the best performance IMHO the location of the listening position is more important than the position of the speakers. It should be no further away from the speakers than the 1/2 way point in the room. This breaks up the timing of the various reflections best. As for bass just move the listening position forwards or backward just a foot or two until you like the bass you hear or add digital room control. The Trinnov Optimizer is the best currently available, the DEQX unit is the best value but has a very steep learning curve. Audiophiles tend to shun these units until they compare active to bypass. Every last audiophile that has heard this in my system has gone out and bought one. The improvement in imaging and overall realism is that obvious. 
If you want to know if your speakers can image beyond themselves get Roger Water's Amused to Death. If I remember correctly the radio should seem as if it is coming from the left side wall and the dog barking should come from the right side wall.

Apologies to all who have responded ... a late edit that I should have caught before sending.  My post says “...does extend beyond the speakers...”. Should have said “...does NOT extend beyond the speakers”
Watch this YouTube video from Dynaudio.  It's got some interesting info in it.  You have great equipment, although, if I had your equipment, I'd choose a speaker from Focal, Von Schweikert, B&W, Wilson, etc.  Some bookshelf Dynaudio speakers would go well with your line stage and amp set up like the Special 40 or Heritage Special.  Go listen to them at a brick and mortar store.
I think the best way to tackle your issues is to move the speakers around until you get the best possible soundstage and frequency response. From there you can make a choice of how much compromise you can accept. 
Typically there is a "competition" between the desirable venue cues on the recording and the undesirable "small room signature" cues of the playback room. In this case apparently the wall behind the speakers is imposing its audible presence atop the venue cues on the recording, thereby limiting soundstage depth.

The earliest reflections are usually the one which most strongly convey "small room signature". On the other hand the later-arriving reflections are in effect the "carriers" of the reverberation tails which are on the recording, so imo we want to use absorption sparingly because early reflection energy becomes late reflection energy after a few bounces. My caution about not overdoing absorption isn’t universal, but is more likely to be applicable to systems with horn speakers, which do not start out with very much off-axis energy to begin with.

I suggest using a mirror up against the front wall to find out exactly where those reflections are coming from. With the mirror flush against the wall when you can see the edges of the horn from the sweet spot, the mirror is in the reflection zone. I suggest either re-directing that reflection energy (using large panels angled such that the reflection misses the sweet spot) OR diffusion (not sure which kind - I’m not an acoustician) OR aggressive absorption (very thick but not necessarily covering any larger area than necessary).

The wall behind the listening position will also be a source of relatively early reflections in this room, may well be worth treating in a similar manner.

I have other ideas about how to tip the "competition" in favor of the venue cues on the recording but they involve projects that I am commercially involved with.    

Where are the columns that they prevent you from pulling the speakers out further?  I can’t picture what you’re talking about. 
Had to read the OP a couple times to make sense of it. The sound stage is narrow- but extends beyond the speakers. Okay, that is not narrow. The sound stage is detailed and precise but not deep. Well that is largely down to the recording. A lot of them are just about as you describe. Some further forward, some with greater depth front to back. They are all over the map. 

These are horns we are talking about. Not a big horn fan, you will have to ask someone who actually used your speakers to know for sure what they are capable of in this area. Also a lot of things like Townshend Podiums and Pods, Synergistic HFT, etc will make big improvements in all the areas you are looking for. Whatever you do, do NOT go multichannel, you will find yourself immersed in pure dreck.
You are experiencing a problem that is inherent in the 'stereo' design. 'In phase' information is only heard between the speakers. Sound coming from outside  the speakers appears only when it is bounced off the walls/ceiling and floor or 'out of phase' information is in the recording. In your set up you have no walls for the sound to bounce off to help create stereo width. That is one of the reasons folks like the short wall more. Depth is highly influenced  by speaker placement (5 to 6 ft is optimum as I think you know) but if it ain't in the recording, and it usually isn't, you won't hear great depth anyway. 

There are devices made to enhance stereo imaging, mostly based on introducing 'out of phase' information that might help, as there are ways of incorporating rear speakers into a two way system which can enhance the sense of sound stage. If you want to hear the effects of out of phase information (only) reverse the plus/minus connections on one speaker. Then you will hear most every thing out of phase - you will note the sound is very spacious but has no central image/focus.  

You have high quality stuff so I suspect you might not want to do this but if your up to a relatively cheap 4 speaker solution investigate the Hafler design. It actually works. But it does have a down side. Doesn't everything? :-)
Did you have these in a different room where you experienced a larger soundstage with them out further? Do you know that they are capable of larger sound? I don't know much about the speakers but I know that all  of them have different points where they excel.  Others have given good info. That said, Why not pull the speakers out a little  further and see what happens? 
You may want to try putting diffusers on the front wall behind and between the speakers, if the esthetics are acceptable. Diffusers tend to enlarge the sound space but in some cases might compromise image specificity. Just need to experiment with the placement (on the wall) to optimize the sound you like.
You've 11 feet. Why not bring them out another foot? Bring them closer together and fire straight ahead. Remove rack from between speakers. 
One possibility is that the image isn't forming as you are almost near field and the driver output hasn't integrated at the listening position.