Hi Carnutt,
I take it you meant your URL to be:
Unfortunately I've tried that circuit before. I've found that doesn't work with at least the JR-421's and JR-652's because they have coupled (or "floating" as some people call them) trainer outputs. In my case it meant that if my interface worked at all, it usually went bongo within a few minutes and needed to be unplugged/plugged-in again.
Steve Lewin was kind enough to put his serial interface for these types of JR's on the web and I have used it successfully. You could probably modify it to work on a parallel port if you need to. Try it out if you're still having problems:
Kind regards,
Anthony.