it was only answer to theory mentioned in
#3 - i.e. USB 3.0 card used with MorphOS like 2.0.
I don't think such card exists.
Now I am using in my X1000 PCIe 3.0 card, it works in linux like 3.0 and not works with MorphOS ( no surprise).
AmigaOS3: Amiga 1200
AmigaOS4: Micro A1-C, AmigaOne XE, Pegasos II, Sam440ep, Sam440ep-flex, Sam460LE, AmigaOneX1000
MorphOS: Efika 5200b, Pegasos I, Sam460LE, Pegasos II, Powerbook G4, Mac Mini, iMac G5, Powermac G5 Quad