Warpdrv, like you, I also value SQ first on a subwoofer and then SPL. I'm still looking for that "almost perfect" DIY 15" sub. Like you, I have the TC 3K sub, great up to 60hz, after that, it drops off quite a bit (lacks the upper bass response I'm looking for), has great build quality but requires a lot of power to run it to its full potential. Before the TC 3k sub, I had the CCS SDX sub, a good all around performer for low-upper bass. It has less lower bass performance and better upper bass when compared to the TC 3K sub, build quality is just o.k. and its SQ is good (not great). Both of these subs were/are in a 3.75cf sealed box and powered by 1,300 watts. I finally think I found the "all around performer" sub for my somewhat small box and moderate power, AV 15H/X subs. Great SQ, awesome upper bass response which can be crossover beyond 200hz, very good quality (build in the U.S.A), affordable, and good low bass. I've been talking to simon5 and John at AE and they have provided me with all the information I requested (including graphs comparing it to other competitors such as CCS, Tempest). I believe this is the best 15" DIY driver in the market right now, the only hard decision I have is whether I should get the AV15H or AV15X (probably the AV15H since it's made for smaller enclousures, but still thinking about it). I will wait for all you guys input on this sub (I think you have the AV15X model) before buying it, but I believe you won't be dissapointed by its performance, specially its SQ.