I've actually done some work (with a buddy) decoding ODB-1 data (from my '95 Camaro) in Linux and sending the data via serial to another VFD. I had hoped to port something to the Empeg early on, but never got around to it. see http://hud.cz28.com for a little more detail and some links.
There's a whole bunch of interesting things that could be done with the diagnostic data sent in the ODB-I stream. I'm not familiar with specifics on ODB-II, except to know that it's hard to find a freely available source on protocol.
I'll be happy to share what I have, if that helps the group.
Dan