Which speakers will fill 5,000 cubic ft coherently

One of the best rooms at RMAF to my ears was quite large and was filled effortlessly by the TAD/Pioneer speakers. They sounded superb and were one of the few rooms there that had me wanting to go back to listen to more. I believe they demand some current though and I didn't notice what amps you are using. If I had a $15k budget to pick speakers at RMAF I absolutely would not hesitate there: TAD. The S1-EX was astoundingly good at $9K, so you'll have change to buy different amps if you need'em. At the show they were driving them with BelCanto Ref1000's which sounded great with a wide range of source material. You could wait for the TAD Reference 1 to come to market but I think the price was going to be around $45k. If you check out the reviewers takes on RMAF and CES this year you'll notice them noted as favorite highlights by many a reviewer as well as folks in the forums here. I have no idea how your wife will feel about their looks, but I cannot imagine not liking the way they reproduce music.

FWIW, Classic Audio Reproductions loudspeakers utilize TAD/Pioneer drivers.

I didn't know that, but they sounded quite good with Ralph's amps at RMAF. I didn't go there because of Springbok10's comment about his wife's distaste for the appearance of horns. For me horns come in all shapes and sizes so I don't really get the blanket rejection. The CAR speakers were gorgeous to my eyes and did sound great, as I said. The TAD Pioneers would still get my vote and $ were I to choose. But, for a huge-room filling sound I do agree that horns are an excellent recommendation and the CAR speakers were outstanding and may indeed to better at filling a huge room. The CAR speakers were playing in one of the largest rooms at the show (greater in volume than Springbok10's) and had no problems filling that room with lifelike sound. The TAD Pioneers were in a large room as well, but the volume of that room was significantly smaller as the ceilings were lower. Still, it was probably equal to the volume of the room Springbok10 is trying to fill. Those speakers just seemed to do everything right.

If you scroll down the page on the Classic Audio Reproductions Contemporary Line page, you will see the T5. These look like traditional box speakers, yet they are 94dB and 16 ohms. I don't believe the T5 use a horn, although the T3 do...and they don't look like traditional horn speakers either.

Have you heard those speakers, Grant? The ones they had at the show that I was responding to were from their "Classic" line. I did not see the "Contemporary" line there(or perhaps I just didn't notice them as the Classics have a very commanding presence). Certainly neither would not fall into any 10" wide limit though. Coincident is a good call. Vienna Acoustics Mahlers perhaps, those also sounded great and are very capable of room-filling sound. Neither impressed me more than the TADs though. Can't recall if they'd fall into the 10" limit, but they'd probably be close.

Despite the fevered claims of some tubaholics, there is a definite advantage to be had by using tubes above 50 Hz and solid stste below that point.

This certainly works well for me (presently) and has worked well in the past as well. I'm currently using my Quicksilver 300B SET amps to push Silverline Sonatinas in a near-field space of moderate volume. Bass without subs is OK, but certainly not visceral. Really good for a 9 watt SET amp compared to others I've heard. I've added an ACI Force XL sub (internal 250W SS amp). At first I found it a bit tricky to integrate, but once integrated the combination is very rewarding. I'd used an ACI Titan in the past (different space and speakers) and found it similarly musical, fast (able to keep up with very sensitive, fast horns), and rewarding. A good friend, who's already chimed in on this thread, tried bi-amping his Maggie 20.1's with a VTL 450 on top and various hi-powered SS amps at the bottom, eventually settling on Parasound JC1's. I got to hear a few different permutations while he was trying to decide on the SS amp, as well as having heard the speakers pushed only by the VTL's. Vertical biamping was a definite improvement in every way for those speakers (though ultimately I felt his room was a bit small for them). The tube/SS combination did work great to my ears. Later on he determined he was not happy with it and went to a second pair of VTL 450's on the bottom. Never got to hear that combo myself, but he liked it much better than the JC1 (ss) on the bottom. Anyway, it certainly can work well IMO.

I'd concur that integrating a good sub effectively with a pair of speakers definitely improves upon soundstaging abilities of the mains in my experience. These improvements have been in the 3-dimensional depth and width of soundstage, and in pinpointing and resolving images in space. It does not, in my experience, however, do anything to increase the "vertical soundstage" (from your original post)...or at least what I'm interpreting your meaning of that to be, which is to say, the scale of imaging. Though more impactful (did I just made that word up) in ways I have never found it to increase the scale of the images produced by the mains. I have certainly heard systems where the scale of the imaging seems larger than life, as it were (I'm assuming this is what you mean by "vertical soundstage"). I'm not sure that I'd appreciate that on a long term basis though. Perhaps. It certainly is a novel experience when I hear it. I wonder if the novelty would wear off. I don't know what qualities speakers/system need to have to pull that off. One such system that impressed me that way consisted of NHT 3.3's and all top-shelf Levinson gear. It wasn't my cup of tea, but it was memorable and impressive in many ways. The scale of everything it reproduced seemed larger than life, and the space it was in was quite large itself, both in footprint and volume. A piano seemed larger than it should in real life and human vocals made the singers feel like giants in some way. If you are looking for this from a speaker/system that doesn't already render something like it already, I don't think a sub will move the sense of scale in that direction. Apologies in advance if I've misinterpreted your meaning.