I recommend you audition the Vandersteen 2Wq. If you stretch your budget a smidge, you can get a pair. I have a pair with the MHP-5 crossovers, and the quality of the bass in my system is incredible. Tunefull, tight, dynamic and clean. Also, they are designed to blend well with any speaker that goes down to 40Hz or lower.
How to select a subwoofer
My current system is shaping up nicely. My next step is to decide on a sub to obtain deeper and tighter bass. My speakers go to 25hz and my room is 14wx22lx9high. I enjoy classical with other genre. The issue of budget is always a question and it should be below 3,0000. Different companies have various setups so I would like suggestions that you enjoy. Thanks, Steve