Try the REL Q-100 E that is for sale here at Audiogon. REL is highly regarded for thir pich and pace, and is cosidered one of the most "musical" subs made today. The Strat II is even better, but $600 is unlikely (though not impossible). $800 is the going rate. Acuujim is right. Go to www.REL.net, and find the Robert Harley review of the Strata II. This will answer you question perfectly.
Subwoofer blues
I need help with narrowing down my sub woofer choice. I have $600.00 to spend and am not sure to buy used or new? My system consists of b&K AVP 1000, Citation 5.1, b&w dm620's and a nakamichi mb-10 using a x-dac. I listen to music but watch a lot of movies as well. I have listened to b&W and a few others but the bass seamed sloppy. PLEASE HELP Best regards Jim