You could meander your way thru System information to "Hardware resources" and check out which DMA channels are available. Labelled 0 to 7 but No.4 is not available as its used by the system. DMA channels should not be shared. It causes crashes. Your sound card is probably using two channels. Maybe there isn't one spare for your optical drive. If it used to work okay then maybe your new sound card has appropriated the channel that was being used on your optical drive. PIO access is pretty slow but sorry I do not have a clue as to the cause.