Newbie needs help

Hi-

I am just beginning to upgrade my system, and have never been at an "audiophile" level (I have various pieces, including an HK surround receiver). I just purchased some used Paradigm Studio 100s for my main system, and will be purchasing new items for a surround system that will go in my basement.

For now, I am planning on putting the HK 5.1 in the basement, but wiring for 7.1. This means I will need somethin get to drive the Studio 100s. I am confused, but think I generally understand that an amp powers the speakers, but you will need a pre-amp to utilize a straight amp, which is why many manufacturers make them in 1 unit. However, I am unclear as to the benefit of breaking these items up.

Also, when it comes to amps, I see reviews for a $1000 amp that seems as good as a $10,000 amp. Frankly, I'm not sure my ears would notice the difference (at least not now). So, I am confused as to what brands to focus on. Names like Krell, Mark Levinson, and Classe, all seem to have loyal followers and high prices. Audiophile never seems to give "bad" reviews, only less positive, and I have not found any other publication that appears to take audio any more seriously.

Sorry for the rambling, but here are my questions: 1. What is the benefit of having a separate amp/preamp over a single system; 2. What is a good name of amp/preamp (or integrated) that is reasonably priced used ($1500 or less +/- total) that could make a difference in the way I hear music? 3. Anyhing else I should know/missed/mis-stated?