There are some very nice DSPs that not only serve as electronic crossovers, but which, with the aid of a measuring microphone, are also capable of achieving a nearly perfect frequency and phase response.
The DEQX DSP has been previously been mentioned
http://www.deqx.com/
and at a recent hi-fi exhibition here in Copenhagen I heard a demonstration of another DSP:
http://www.holmacoustics.com/dspre1_introduction.php
The problem is that they are so expensive. The 3-way stereo version of the Holm Acoustics DSP thus costs 40.000 DKK (approx. $6800).
Being a computer scientist with some knowledge of DSP, I could programme a DSP myself. I just need a device with suitable analogue og digital inputs and outputs, and with a USB or similar port such that programmes can be transferred from my PC to the DSP.
I would like to hear from members with a knowledge of user programmable DSPs.