Not exactly what I was looking for, but definitely in the cards to try.
it seems someone made a comment back about 14 years ago on some website that Apple had a deal with harman/kardon that only allowed the iSub to work on the iMac and PowerMac G3 B&W, unsure if it'll work on the beige, though.
so it seems I solved my own issue in the midst of confusion. Apparently the Sub shows up all proper in the system profiler, just doesn't activate and show up under the Sounds control panel.