Nicholas_1213 hi
Unsound is correct about the Mac.
It would be good to get hold of a impedance/phase graph of your speakers, this will then give a good idea for either the Krell or Pass. If your speakers are a hard load then the Krell would be the way, if not then either would do and will depend if you like Mosfet sound (Pass) or Krell sound (Bi-Polar).
This is mostly but not always the case depending on circuit and speakers.
Mosfets tend to be sweeter more laid back.
Bi-Polars more punchy and up front, can be just as sweet with lots of Class A bias.
Cheers George