What is amp's watts-per-channel exceeds speaker?

I want to buy an Outlaw Audio 950 pre/pro along with their Model 770 7-channel Amplifier. The amp puts out 200Wpc.

I have YET to buy speakers, and I have only $1,000 above the pre/amp to buy speakers. I planned on using all $1k for a decent pair of fronts, and try to use my existing 5.1 speakers (these were on a Sony receiver) to fill in the other holes in this new 7.1 system.

My proposed speaker setup:

Fronts: Not yet decided
Rears: Celestion Impact 30, 4 ohm, max 150W
2nd Surrounds: Celestion "Little 1", 8 ohm, 10-50W
Center: MB Quart Center, 6 ohm, 125W
Sub: Velodyne self powered 10"

Here's my newbie question: What happens to my existing speakers when I drive them with a 200Wpc amp? Does the amp step down automatically? From the pre/pro, can I tell them amp to step down the wattage?

Thanks, Greg