Michael McMasters got back to me.  He doesn't know anyone who's used it with a 512k or a Plus.  Unfortunately it was my last one and I already stuck it into and SE/30 that's going to be shipped out.

In any event, when I get another one, he said I can hook it up via USB and while it's connected to the 512k simultaneously, then run a utility to capture the data in real time and save it to a log.

I'll send him the log and he's going to analyze it, see what's going on.