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Question

"I was told by a best buy salesperson that there was a 7 channel receiver, that when hooked up to a 5 channel receiver would carry-over the power from the 2 UNUSED channels to the other 5 channels. Does anyone know what receiver he was talking about???pls help. In otherwords the unused wattage from the other two channels would be divided up between the other channels..He said its the only receiver that does this..!"

Answer 1

It's basically simple EE theory.   The power supply in the AVR is only capable of delivering so much usable power to drive the load, i.e. loudspeakers.   So the fewer channels that are being driven allows more power to be fed to the channels that are active.   All the channels are tied to the same power grid in the unit. 
It's one reason that usually spec units with two channels being driven if you look closely.   With two channels it is much easier to meet the published 100wpc spec.   If you ever look at hardware reviews of AVR it becomes apparent right away when driving up to 7 speakers the available watts per channel drops significantly.  Good news though most of those tests create conditions that typically don't occur with typical source material (driving 7 channels 20Hz-20kHz in phase at the same time).  Even those conditions cause even highend units to kick into protection mode that limits the current being pulled from the power supply so it does not burst into flames.
With most modern soundtracks 95% of the content is being delivered to your front three speakers.   The surrounds are rarely heavily active for most films.
So the salesmen was not lying, but what he was explaining is just a basic principle on how the AVR operates and it something that manufacturers don't put into marketing material.   If you look closely at the specs you can see that even on 7 channel AVRs that the power is usually spec'd for only driving two channels.  If they spec'd all 7 channels running it does not generate an exciting number for marketing to tout.
WPC is also not the whole story... you could spec a power figure of 100WPC easily  but if the total harmonic distortion was on on the order of 10% it would not sound too good.   Look for a THD of 0.1% or less with power figure the manufacturer is claiming.   Also it is not unusual to see a high WPC quoted with no THD on the box, but a much lower one on the spec page with a reasonable THD.   That's because the FTC regulates how power figure has to be stated. 
So this is my general advice to anyone buying an AVR:
1. Get the features you need... proper number of ins and outs for your application and the proper type(HDMI, component, etc), DSP, etc
2. Get the highest WPC with the lowest THD of the models that fit your features needed in #1 and fits your budget.