You have a working (SCSI) Fastlane Z3 in an A4000? That is virtually unheard of. They are such finicky cards that I named their compatibility issues the "Fastlane Blues." They seem to come mated for life to only one A4000, and in my experience I tried 2 different Fastlanes in 3 different A4000D's and 2 A4000Ts. They work as partially filled RAM boards, but never SCSI.
I would sell your fastlane and the daughter board as a unit and keep the Mediator. Then take the income and invest in an A4091 or FastATA 4000.
This only my opinion, but having explored the forums and the web for weeks, plus burning a set of 8.5 ROMs in my attempt to get one working, I determined that Resistance is Futile, and your time will be assimilated.
I own 4 of these cards and have used them in every z3 amiga(rev 2.2 to 2.4), they work fine, including scsi, anyhow they work great. not sure why u had such experiences. It has a work around for buster 9 and even worked fine with it.
