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Paul:
Your speakers will have a "sensitivity" rating, expressed in decibels at 1 watt/meter. This is what is meant by efficiency. For example, looking at a product sheet for a KEF Q7, I see a sensitivity rating of 91 db. This is considered very efficient and would not need a lot of amplifier power to reach good volumes. The manufacturer also says that the Q7 needs an amplifier between 15 and 175 wpc.
Conversely, I have Magnepan MMGs, which have a sensitivity (generously rated) of 84 db. This is very inefficient and requires a strong amp which can also drive its low impedence (3.7 - 4.0 ohms) load. You need to start at about a good 80 watts with a high current power supply to get good sound out of the MMGs.
So, your speakers sensitivity rating will tell you a lot about your needs.
However, another factor is whether your receiver actually puts out its rated power. I can tell you that it doesn't. Pioneer, like Sony and a few other manufacturers, fudge their power ratings by raising the voltage in order to get the 100 wpc they claim (Wattage is a function of voltage and current--raise the voltage and you raise the watts). However, when run by the proper voltage (which is what your electrical company delivers to you), the receiver cannot come close to its rated power. Furthermore, that 100 wpc is only when two channels are driven, not five, six or even seven channels. I have not seen a product review of the 811 S, but based upon other receivers in the same price range that have been tested, the 811 S probably won't do more than 45-55 wpc with all channels driven. Typically, when you drive all channels at the same time, the power supply gets over-taxed and that is when you can get amp clipping that can damage your speakers. In this regard, your friend is probably right.
Of the major receiver manufacturers, I am only aware of three that rate their receivers with all channels driven instead of two channels at a time: NAD, Harman/Kardon, and Marantz. The major audio magazines both here and in the UK have confirmed that NAD and H/K exceed their power ratings. Marantz, however, is still a question (the new models have not had a test reported yet). People are always amazed, for example, at how a 50 wpc NAD can sound louder and cleaner than another brands "100 wpc" receiver.
Your response, however, may well be over-kill. I love the Outlaws, but you could easily do well with a high quality receiver (any NAD or a H/K 525) rather than Outlaw monoblocks. If you want to go the separates route, I would recommend the new Outlaw 7100. Yes, it is only 100 wpc, but it is an honest 100 wpc and will make you wonder how Pioneer could ever rate their receiver as 100 wpc (good question). I would suggest that you find an NAD dealer and take home a model 752 receiver (80 wpc x 6) home for a few days as a benchmark to see what you think. If you find you still need more power, then return the NAD and get the Outlaws (950/7100).
Good luck
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