List of sites with firmware updates for FireWire devices
Note, firmware should be updated by service personnel, not end-users. Nevertheless, here are some links to firmware update utilities and firmware image files. They typically require Windows. Some vendors also provide updaters which run under OS X.
SBP-2 (storage) devices
You may try to contact Initio directly to get firmwares for Initio bridges other than INIC-1430.
Very old Prolific firmware needs to be updated with the v2.0.4 utility first. After that, the newer utility and the newest ROM can apparently be used for the final update. The updater should show the presently installed firmware version; after that you should be able to upload new firmware to the device or abort.