Wasn't the old Comm Slot a PDS Card slot?

That may be the issue. Does the IIe card work with the Ethernet in it? or can you get an IP Address, either MacTCP or TCP/IP with the IIe card in it?

I know the CommSlot II on the PCI powermacs is essentially a re-wired/custom implementation of the PCI slot, but I was pretty sure the old CommSlot was an extension of the PDS bus