I think you just answered your own question, pardner.
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Have you considered separate amps for only the front channels and let the AVR handle the surrounds? Since the surround channels rarely get driven hard, it would be a more economical solution. You could even get away with the AVR handling the center. With it driving only 3 channels it should be able to put out the volume you want. This will make your setup better for music too.
It's not just a power issue, it's a noise floor issue. I don't like the hashy sonic mess and compression you get when you have low-level analog and digital decoding components sharing a chassis with all the vibration (60 Hz) and heat you get with what should be a high current 7-channel amp.
I have my power amps on a separate shelf from my pre/pro. True, you can get 150-to-190 wpc A/V receivers, but not only are you adding all that jazz to a low signal chassis, in most cases they compromise the power supply to get everything to fit. And that's another source of compression you get with a receiver.
Look at the specs and test reports for most A/V receivers. They rate the power with one channel driven, and often with a 1KHz test tone (no bandwidth) at 1% distortion. An A/V receiver tested at 90 wpc under those circumstances only puts out about 43 wpc with all channels driven, 20-20KHz, at 0.1% distortion. And I've seen enough Home Theater mag test reports to prove it.
Most A/V receivers rated at 125 wpc will not have anywhere near the balls of a similarly rated separate amp from Adcom, Outlaw, or Parasound, never mind the high-priced spread.
Yup if you add a beefy 2 channle amp from any number of makers your AV unit should be ok for center and surrounds. While I dont have a reciever I do run a hunble 6 channel Rotel which can be bridged up to 3 channels so I bridge the center only and use stock power for all surrounds. I get 120W to center and 60 to all 4 surrounds BUT I only roll them off at 80Hz, if you intend to run more full range speakers that isnt likely to be enough power but for me in my 14X25 HT I have never felt I need more power, my surrounds are 92db efficient if I recall. I do listen loud and have a picky personality but again for HT its fine for me.............music is another animal.
I added an external amp to my receiver and it got a new lease on life. I'm still using a ProLogic "dolby-digital ready" receiver as my main unit (Sony GA7-ES). As such, it does not have equal power to all five channels, which was normal for the ProLogic specs in those days. It has beefy parallel push-pull amps for the front three channels (90W RMS) but fairly pedestrian (non-high current) 40W power for the rears.
Sony thoughtfully provided a "power swap" feature on the 7ES which when engaged, routes power from the main 90W amps to the surrounds and lets you add a 3-channel external amp to drive the fronts. I chose an Arcam Alpha 10p x 3 channel amp at 100W and now have matching power to all three front speakers with the Sony just idling on the rears. I bought the Arcam amp used on Audiogon for a fair price and it's really made a difference in my system. And I can still use it if I move beyond the 7ES to a newer receiver or processor. -jz