I built this interface this morning and it's working for both JP1 (8910) and JP1.3 (15-100). Of course, you can only talk to one remote at a time and the JP1 serial only works with IR, or I can't figure out how to select JP1 serial on RMIR. Also, the JP1 serial only works on real comm ports and not USB emulated comm ports. Furthermore, since IR hardcodes the comm port addresses, it only works if for motherboard comm ports unless you patch IR with the actual address of the comm port.
A.A.