Couple of months ago i bought a Apexi PFC for an ep82, so after a couple of months i went about and finally made my own adapter harness so it would fit an ep91. I can now confirm that an ep82 Apexi pfc will work on an ep91 as long as you have an approrite wiring harness.
I gutted a connector out of a old 4afe ecu then using the ep82 figured out what the PFC pinout was. Its not a diy job for those who dont have any patience, it roughly took me about 12hrs of work, the most difficult bit was soldering the cable to the pinouts on the connector. That took the majority of my time.