@Arnie: Never mind. I already ordered a USB 2.0 cable.
@spidi: Can i use the adapter with Amiga firmware flashed on a C64 too or is it mandatory to flash the C64 firmware? Any chances that the original Sega Mega Drive 6-Button pad (MK-1653-50) + RetroLink USB adapter works too (Amiga 1200 as CD32 pad)?