first question, what do you want to listen to?
unless you have 5.1 music, you will need some simulation software / hardware to send audio to the centre and rear speakers. and unless it just copies the front audio to other speakers ive never been that impressed with surround sound emulators.
normal music is 2.0 (eg L + R ONLY)
movies 5.1 or 7.1
most pc's if they have digital outputs can pass the AC3 audio thru that to a 5.1 amp, or you can use the analogue outputs to separate amps and tune it by ear.