help me maximize my sonus faber concertinos

Where can I get the biggest improvement for my current system?

Sonus Faber Concertinos
Velodyne VA 1012 II subwoofer
NAD T750 receiver
Panasonic DVD-A310 (doubles as CD player)
DH Labs BL1 interconnects
Analysis Plus Oval 12 speaker cable

I definitely want to keep the speakers and cabling, everything else is fair game. I mostly listen to classical, some rock and pop, an occasional movie. Most important system consideration: must be musical/exciting/emotionally involving; detail and imaging are next.

Main Problem: the sub doesn't integrate well. It has a fixed, non-defeatable, 85hZ crossover. My receiver sends a FULL signal to the mains plus everything below 100hZ to the sub. This makes the bass very muddy because the Concertinos go down to 55hZ.

Solutions:
- get a receiver with bass management
- get a new sub with a variable crossover for bass fill
- get an amp and use the sub's crossover with LR pre-outs
- forget your bass problem and get a real CD/SACD player
- something I haven't thought of

I don't want to use the sub's crossover with speaker inputs/outputs because it has spring clips which preclude the use of quality speaker cables. Also, I read that this way sucks.

Please recommend specific brands, models, and a crossover frequency. Ideally I would like budget $500 for this and absolutely not over a $1000. Used is OK. I am limited in space and would prefer to replace equipment, but if I need to make space for additional hardware, so be it

Thanks,

Gene