Is there a reason your not using the ASIO drivers from M-Audio. (Probably so you could use the second audio device)I understand that.
Using 2 different types of audio capture devices might be causing timing problems leading to the crash.
Some things that may help would be to have more ram memory while using a 64 bit OS. A second hard drive for data only.
I remember hearing that the M-audio Ultra 8 device can be used with a second Ultra 8 to record up to 16 inputs at once.