I think you misunderstood the amp ratings. 2x100 means 2 channels at 100 watts each. So your fronts would get 100 each, but you 6 ohm center and surrounds would get 125 each. In order to use these with your current setup, your receiver needs to have pre-outs for all 5 channels.

Also, powering the center only requires one amp, so if you got the two channel amp, one of the channels would go unused.