I feel your pain. Sitting in a 28x30x8 room myself and it is open to the stairway and the entire upper floor from there. Archaea speaks the truth. It hurts... but he is being honest.
I started with an Outlaw -EX approximately 8 feet from my couch in the 2nd best spot according to my sub crawl adventure. This is a beast of a sub compared to what I used before and it hurt to spend the money. I did it on the advise of members here (Archaea and others) and I'm glad I listened. $600 for a sub and it was JUST OK! The bass varied wildly just by moving 1 cushion over on the couch. BUT I fear anything smaller, like I had planned, would have just been lost in the room. MAYBE a PA-150 would have worked if I was willing to give on the lower end.
I've just added a RW-12D myself until I can save up for a 2nd EX and/or maybe a 2nd RW-12 also. At this point I have the 12D in the old spot (about 8' away) and the EX corner loaded after WAF approval (again about 8' away). So... ~$900 later and I at least have 'good' and somewhat smooth bass on my sectional. I would still like more... but for the time being at least I have some noticeable spl output and only about +-2dB from one end of the couch to the other.
IF you can keep them close, and/or add another RW-12 or better, you might be ok. But don't expect window shaking or knick knacks falling.