It really depends on the efficency of your speakers. Most surrounds only need about 20 watts or less to drive them. Remember they are fill for the movie and unless you have purchased some larger drivers for the surround channels or bipole/dipoles with alot of drivers, they are usually not power hungry. Besides the subwoofer, Centers are usually about 60% of the movie, 25% for the fronts and 15% for the surrounds.

Again it depends on your speakers...