depends on the design of the amp. One amp that I have lusted for so long but didnt have a chance to own one due to its brand new cost is the Enlightened Audio Designs Powermaster series. it has what they patented as "Dynamic Energy Steering" which channels all the power of the 5 channels into two channels when used in stereo only. The Powermaster 500 runs 100watts x 5 channels RMS but when used in 2 channels it delivers 300watts x 2 RMS.
just the faceplate of the amp alone screams "SERIOUS GEAR"
![](http://www.nobleelectronics.net/PM8300-in.jpg)