I could be wrong, but I'm pretty sure Aptus 54 never existed.
For sure Aptus 5 before Aptus II 5 never existed.
I've never heard of DL-22.
There are three backs:
Aptus 22 - original, FW400,
Aptus 54s - faster, more noise, FW800
Aptus II 5 A.K.A, Aptus II 22, Mamiya DM-22 - faster, less noise, FW800, brighter LCD, newer UI, better colors