Importance of Amplifier versus Preamp?

Read the Audiogon forums until you understand all things about impedance between components, impedence curves in speakers, efficiency/sensitivity of speakers, balanced vs unbalanced components and the different types of sources and their benefits. Just put in keywords and go from there. If you learn as much as possible before making a decision it will be a better decision.
I might also suggest a copy of Get Better Sound from Jim Smith. He covers a lot of things about speaker/room interactions. Have fun, it can be a lot of fun if you don't make any big mistakes.
It may seem like a lot but it begins to fall in place at some point.