If you have to get a sub I would go to audioc.com and get a "quake" or stretch for the "titan" as one other said. I don't have experience with either though, What I can say from experience is that a better pair of main speakers is the way to get better bass (while maybe not being as deep, definately more coherent and cleaner), not to mention everything else will be better. Sell the infinity's and take that money, plus your $500 budget and buy a nice set of mains. The BiroMod Wharfedale Diamond 7.2's at www.avahifi.com for $250 actually look tbetter than alot of stuff out there, and you could probably get your sub in the end too if your just dying to have one and it'll all be within your budget. I own the biro L/1's and those are very nice and I'm not running a sub yet with all my hybrid tube/solid-state electronics. My general opinion on the application of most subs is that they are a cheap fix for a not-so-good pair of front speakers and/or an amplifier(s) that are underdamped in the low-frequencies. And then of course there are sloppy DACs. If you got your bases covered on all that then a sub may be a *musical* choice. If your a music person, you'll probably be happier w/ just a better pair of speakers. Not to mention, you might want to get a nice little integrated amp (nad?). You could probably do a complete overhall, for your sub price range plus what you make off selling others. Keep in mind I'm not trying to divert you in any way, I'm just saying you'll get the better bass your wanting, not to mention everything else. But I, personnaly, wouldn't buy a sub. The marantz cd-67's used are running in the low 2's used as are good integrateds. I actually got my sister a pair of rotel pieces for $200 each demo's, cd player and 35wpc integrated. I can't say they are the best budget pieces, but they were 'new' and they matched. Good luck!