Jack, what you are 'matching' for the most part is pre-amp out put impedence (low is good) and amp input impedence (high is good). Too high an output impedence from the pre-amp and too low an input impedence in an amp is not so good, it will roll off frequency extension, highs and lows mostly noticible in the lows. The other thing you want to consider, and involves speaker efficiency is the amount of gain from the pre-amp, this input sensitivity of the amp, and the speaker efficiency. You don't need (or want) a lot of gain from a pre-amp if you have an amp which has high sensitivity (a low(er) number) and or speakers that have high efficency. Its all a balancing thing and your dealer should be able to help you to get the 'numbers' all lined up.
Apart from that the only other thing to consider, and actually the most difficult for lots of folks, is tonal synergy through out the system and making sure that the clarity/resolution levels in your other components are not impeded by the sonics of the pre-amp you have chosen.
The good news though the sonics of the pre-amp are, or at least should be, the least problematic in setting up a system in the first place, and less difficult to introduce to an existing system.
I hope that helps you some.
