Sashav,
Is this the drill?
You'll take the digital out from a disc player or server to a digital x-over unit that outputs 3 pairs of digital out: stereo digital high, stereo digital mid, and stereo digital low. From there you want to use (the equivalent of) 3 stereo DACs that output a balanced analog signal: one for the the stereo lowpass, one for the stero mids and one for the stereo highs. Then you want to take those 6 balanced analag outputs into 6 balanced inputs on the preamp you're asking about. You need a single volume control to move the 3 stereo signals in unison.
The idea being that you want to keep volume control out of the digital domain to retain resolution.
I think that the top model Tact and DEQX units offer both the dig x-over and analog preamp sections that you're seeking in a single box, and both are available with XLR out. There are a bunch of good pre-pros that also offer this as an integrated solution.
FWIW, philosophically, this feels to me like a great way to go. I've been looking at a related approach using 2 way speakes similarly tethered to subs, but that still leaves one analog x-over in the path. I like your approach even better, but I'm not ready to do the the DIY thing and there are few commercial choices (Merdian, Salk?) available employing this approach.
Good Luck and keep us posted on the progress of your project. It sounds interesting.
Marty
