<font color='#000000'>If you're demoing at Circuit City and such, the subs sound like crap because 1) they're poorly set up, and 2) many are indeed crap.
To maximize your chance of good musicality and to minimize the hassle, go with an integrated sub/bookshelf system from the same manufacturer. Good brands like PSB, Axiom, Paradigm, and that Japanese outfit that also makes motorcycles are worth investigating for a start. And they'll come with instructions!
Heck, since you already have PSBs (assuming you like them) why not just get a PSB sub? They make four models. Check their Website.
Sucessfully integrating an aftermarket sub, even excellent ones like Velodynes, Carvers, and Hsus takes some futzing and knowledge.
Don't know your particular amp so I can't speak to hookup. If it has preamp only output jacks in additon to the speaker hookups then you're probably OK.
And just to confuse you: do you *really* need a sub in your small room? Or would it be overkill? Good full range speakers might do the trick. All the mfrs. above and many more make compact floor standing full ranges with good bass extension that would do nicely without overwhelming the room. I was looking at some used PSB Image 4T's for my 10' x 14' den before the dipole/DIY bug bit me.</font>