I never got my G-Rex working on my Rev.0 BPPC.
KDH told me I could send it to DCE to be upgraded to rev.2 but I didn't feel comfortable doing that so in the end I returned the G-Rex to KDH and got a mediator instead.
I don't know anyone who uses a G-Rex with a revision 0 BPPC. Maybe they exist but who knows.
A Mac mini is a good choice if you want to switch. It will certainly be a lot less trouble to keep running than your A1200.
Or you could wait for one of the new A1200 accelerator / busboard combinations from ACK or Elbox, or get a mediator.
