I use that same clock for my 2408 MK3 with a G5 and it works great. It also clocks my HD24 when everything is running together. Have you checked over at www.unicornation.com
the motu forum?
I have heard that motu interfaces work differently in PC's, and that the BL modded versions with the clock mod have issues with external clock sync. That doesn't help you, but it might help somebody.