If you have the resources and the ambition you can put two PDS cards into the IIsi at once.

All this and a 25mhz modified board too (not my mod, just got lucky to find one).

I have a PDS-based SuperMac 8-24 PDQ card (which I think is just a Nubus card hack) with it's PDS riser, a 68882 FPU, and an Asante PDS ethernet card.

There is just enough space to mount an AUI 15-pin connector (with 10 Base-T converter) along with the video connector in the single slot opening.