Thanks, all.

I did wind up going the OSC route. I haven't touched this material in a while, so it took a bit for my brain to adjust in the darkness.

But, yes:

In Isadora: OSC Transmitter to ETC Eos on the same Mac. Gadget is now outputting correct DMX as tested via a DMX tester. Fabulous!

Final hurdle was switching the OSC transmitter to "on" in Isadora.

Thanks for the support!

@gunther Thanks !

@woland

that's great, thanks you so much !