Good musical sub under $500

I need to replace my crappy old AudioSource sub, my listening room is 12'X14' x9', hardwood floors (livingroom, not sure if furniture such as couches effect subs in absorbing sound as it does with mids & tweeters) . It will be 70% music so a accurate tight bass is a must,. It will be matched up with my NAD T752 A/V and Paradigm Studio 20v3s up front. MY present Audiosource I've had for years has to be turned to full volume just to add some low-end (Crossed over at 80, anything higher and you get vocals and such coming out of it, really crappy as I said lol). I had ordered a Velodyne DLS-3750R earlier in the week(cancelled my order) the more I read up on them it seems they are rather boomy and velodyne's good subs are the higher end stuff which are out of my price range. Used is ok as long as it's from a reputable dealer or owner (ebay is definitely out, really don't trust high end stuff from there). Suggestions?