I've come up with a way to make standard PC drives work in the Ensoniq EPS.
As one might expect, it requires modification of the drive's circuitry. The good news is that it doesn't require modifications to the EPS unit, nor does it require any workarounds. They function as drop-in replacements.
I suspect that these drives might work in the EPS-16+, too, but I don't have one to test them on.
I'm trying to get a feel for how much interest there would be if I were to offer these modified drives for sale...