I just had a look in my other machine (Dell Dimension 2400, 2.66 Celeron, has a single DVD/CDRW drive installed in it from standard)

That has two 4-pin audio ports on the motherboard as I would expect, but there is no cable attached to the drive The only things plugged into it are the IDE ribbon and the power harness. No analog audio cable or S/PDIF cable

WTF is going on there......