I recently had this same problem with an Imacon Flextight precision II. Only I don't have a G5 I have an old 350Mhz G4, and I was able to get the Imacon working again with the RATOC adapter, but not without some help from their very good customer email support. The first thing I discovered was that getting it to work with 10.3.x was practically impossible, so Ratoc told me that it would work on 10.4, and it did. This is what I had to do. Upgrade the OS to 10.4, downgrade the Ratoc adapter's firmware to 1.23 (it comes with 1.33) and run an older version of the flexcolor software 4.0.1. This did the trick. Also note that I'm running an AC adapter on the SCSI to Firewire adapter, and the device needs a SCSI-1 to Ultra SCSI adapter on top of that, which makes it a really tight squeeze for your firewire cable, but it can be done! Good Luck.
this page will have everything you need to get going
http://shop.store.yahoo.com/firewireshop/firfirscsico.html