Just an observation: I tried setting NEC2500 as slave, and it wouldn’t even detect properly in BIOS. The master drive was Pioneer DVD ROM DVD-116.
When I swapped them, everything was fine.
I tried setting CS (cable select) both ways and they weren’t being detected at all.
I guess slavery is out then.
I usually used the Master drive for reading, the Slave for burning.
I guess this time I’ll have to do it the other way.