Ahh OK I see. The Rock is a great platform and the arm damping on the trough really makes it shine, albeit at the expense of some useability. The Terminator may well work fine on it though... It definitely needs to be tried ! I'd look for a decent cheap mm - maybe an Ortofon or Nagaoka - and take it from there.
As to the others - well, buying secondhand has it's risk but can, in some ways, be a better bet - you can try things and if you buy wisely (trusted sellers, good condition, not so obscure as to be unsellable) if you don't like you can sell on again an far less loss than on something new. It can be fun too. I've not gone far wrong when choosing kit by reading reviews and forum opinions - you get a good idea of how kit performs and a sense of how they might go together.