I know this group is dead but thought I would post here anyways. I played around with an Arduino Mega 2560 and replaced the AtomPro28 processor on a four channel CVS to see what it would do. The SPI update rate for the DACs is considerably faster since the Arduino uses native hardware support in the AVR. I've only benchmarked one program between the Arduino and the AtomPro28 which was a tight loop stepping through 128 semitone CVs.
I don't know that I will go anywhere with this as I have enough programmable modules and the speed difference wasn't that compelling but it was an interesting exercise. Some details and photos on my Arduino CVS page.
http://modularsynthesis.com/arduino/arduino-cvs/arduino-cvs.htmDave