The Bryston 10B (that I mentioned above) is likely your best choice for active analog crossover to keep the resolution of your preamp. It has fully discrete analog circuits (probably running in Class A mode) and an excellent power supply. Input impedance is 15k. There’s one on audiogon for $995. They typically sell for well over a thousand.
There’s a Krell KBX for $1360 on ebay. It will probably sound more relaxed than the Bryston, but would probably need to be recapped. Also, the front dials do not show crossover frequency steps, so it will be impossible to determine actual crossover frequency without some sort of mic or line measurement device.
If you want to go cheaper, you could look at a new Ashly XR-1001, but you’d have to use some special cables (either XLR or 1/4" TRS). It is a pro audio crossover, but it is still fully analog (as opposed to digital/dsp like most of the pro audio crossovers nowadays). Input impedance is 20k ohms balanced (this is probably 10k ohms single ended as I can see a 10k ohm resistor on the input of each XLR leg). You can pick it up for $250 at many musician websites (sweetwater, parts express, etc.).
http://s298.photobucket.com/user/maryna1109/media/music/DSCN8468.jpg.html?t=1254515907
The Ashly is not going to be anywhere near the resolution/quality of the Bryston. If I did the Ashly, I would be making significant mods to it. First, Ashly likes to supply power at +/-18V, which is on the high side for normal op amp circuits, but they use normal 7818/7918 regulators. I would be doing the following:
- replace the 7818/7918 monolithic regulators with Sparkos Labs discrete regulators and drop the voltage down to +/-15V.
- Put in the largest power supply capacitors I could fit in the board/chassis (currently they are only 2 x 1000uf).
- Swap out all the op amps with AD797 on dual-channel DIP8 adapters.
- Solder 47uf Muse + 0.01uf metallized poly directly to the power pins on each op amp.
- Replace all the op amp negative feedback caps with film/foil or silver mica.
This is probably $450 worth of components (not including labor).
I’ve seen dbx, Ashly and other analog pro audio crossovers.