Two subs or not Two subs?

My single REL was never directional, but I added a second one (also costing 200 bucks used), a Q108II…it's all better as the RELs are dissimilar (an 8" down firing, and a 10" forward firing) and complementary. 

For music, I always use two subs. They image — they reshape the soundstage as it really was. I have a live Jazz recording I use as a reference — for years, with a single sub, bass player was way back in the soundstage, center stage. Adding the second sub, he moved 10 feet to the left. It was more than just one instrument moving — his relationship to other players and their collective energy was more vibrant, and the archictecture of the nightclub became a real place.

A single sub, if located properly AND large enough to excite the OPs 3000 cubic feet would be fine.
My room, larger in all dimensions, and irregularly shaped, is fine with a 12" sub with 'only' 250 watts. It is a HSU Research VTF 2/III.
And even though not rated, it will reproduce the 16hz pedal tone on the Saint Saens symphony #3, 'with organ'.

You can't localize much below 80hz in a normal home space. Like the OK restaurant doing land office business? Location, Location, Location.

The question for me, when I bought, was if I could afford a pair of subs or a single better sub? If I'd had the $$$, the purchase of a pair would have been online.

You can go to AVS forums in the subwoofer section and look for the ancient subwoofer shootout thread.
Look for the best used sub that $800 can buy. SVS sometimes has scratch and dents for a good price.
For this kind of money you should be able to get amplified Hz just below 20.
Just be warned; I set a $ limit then eventually doubled it.
A quality powered sub will last a lifetime.
No regrets.

I used a single REL for quite some time but always found it directional, no matter where I placed it in the room. Meaning, that I could always detect just where the bass source was located.
I now have a pair of ML Descenti's and the integration with the main 2 channel speakers is great and they are so much more 'tuneable' than REL's. Descenti are not cheap but highly recommended.

Are Rel's the best option for high level connections right off of the amp or are their other brands with the same type of connection that work better. Price range $0-$800

I would buy one good sub over two OK subs any day of the week.

Used RELs (ar any good sub) can be the way to go...I have a room about the size of the one described, and my single REL Q150E (circa 2001 10" forward firing) sounds great set around a third of its volume knob setting...adjusted slightly up or down here and there depending on the recording (I put a "chicken head" knob on the gain pot so I can easily tell what's what without turning the sub around). 2 RELs like this seem like overkill, but I'd buy another Q150E if I found a used one cheap enough just because I like it so much. Interesting article I read recently in a UK hifi mag about a REL sub...the writer was listening to some mandolin music and took the sub in and out of the system...you wouldn't think mandolins would have any low frequency information, but the music sounded much better with the sub on...go figure...I've done similar experiments and am amazed at how low the output on a sub can be and still add MOJO to whatever I'm listening to.

In the review of the T series I read the lowest crossover point was 60 Hz; they must have corrected this on the T3; something like this one: http://www.audiogon.com/cgi-bin/cls.pl?homesubw&1321761237&/Rel-Stadium-II-fast--detailed- would be all you would ever need. One was just sold for $795. I used one of the Stadium 2s for a while before getting a second one; I would rather have one better one than 2 lesser ones. The smaller S series are also good.

30hz to 120hz is quite good. Stan is probable talking about a used sub that may be discontinued. Look on the classified adds here on AGon.

Stanwal
I don't see a S series sub on REl's site is it discontinued.Also why would the t-3's variable crossover(30-120hrz.) be considered to high?

Usually two subs work better for music , as opposed to home theater . The only issue with two is there allot harder to set up properly , phasing and such .

T series is for home theater; crosses over much higher than the S series. Get one S series and see how you like it; one may be all you need.

I agree with Zman.
If you buy 1 sub first, get some long el'cheepo (Rat Shack) sub cables and move it all around the room. You may be surprised at where it sounds the best.
Good luck

In a room that size, two subs might be better than one.
Adding bass traps would make a much better improvement if you do add two subs.
I use one sub, but my room is much smaller than yours.
Another idea, try one sub first, and if you feel like it's not ballanced, then get another. With the room being deep at the listoning position, one sub might work fine.
Good luck and keep us posted.