What do I need to consider when buying amp and sub

There is another thread talking about the JL sub which I did not want to hijack. Reading the thread made me think of things I should be considering before I purchase either the sub or amplifier.

1. What kind of output's, or bypasses, should I be looking for in an integrated amplifier?

2. What should I be looking for when I purchase a sub in regards to integration to my 2 channel system?

I like the JL sub and my local dealer sells them. The Amps I have been looking at are Musical Fidelity and McIntosh.

Thanks for your help.
Jeff