Nice FAQ - I once asked an NHT engineer about what power he recommends for their speakers, and I got the response "power is tricky thing" - he was right! So kudos for stepping into a potential minefield. Thought I might add my $.02 to the discussion as well.
- "Best sound for my budget?" Purely my opinion, FWIW: better speakers first. Good speakers with a decent AVR are likely to sound better than average speakers with a good amp. Balance is good, but the scale should favor speaker quality over power. Good advice for the less informed, perhaps?
- There are reasons other than volume (loudness) that can justify a higher-rated amp. A lot of folks pick up way more power than they need (i.e. they aren't trying to make their system louder) for the purpose of improved dynamics. You might consider mentioning something about capacitance (more power "ready to go" in a higher-rated amp) and how a 500W amp can deliver more of a "kick" or punchier sound than a 100W amp at a given loudness. While the need for power is often overstated, many claim to hear the difference with more power, especially in the dynamics. Does that make it so? No, but this view is widespread enough for consideration. I've never done A/B testing myself and can't comment.
- Might also correlate the term "headroom" with the lower distortion you'd expect to see from a higher-rated amp at a given loudness.
- I'd clarify the "power damages speakers" discussion. Driving speakers with too much current (power) can damage them. Using a higher-rated amp will not, by itself, damage speakers. Certainly there's a higher potential for damage with more wattage, because the amp can drive the speaker louder. Assuming no clipping, at 100dB, a 1000W amp is no more harmful than a 100W amp. (Likely less, considering the lower distortion.) The reason a 1000W amp is a bad choice for a 100W-rated speaker is that some jackass can come along and crank your stereo to the max: a 100W amp will do bad things in this scenario, but a 1000W amp will likely blow the speaker outright.
- In absolute terms, ACD measurements aren't helpful as they don't accurately represent how power is used in a 5.1/7.1 setup ... but in relative terms, they DO allow us to compare one amp to another. In that sense, ACD is helpful for judging amps and more manufacturers should include it. Another way to look at it: if an ACD measurement is given, it's likely a much better amp than one without an ACD figure. As you mentioned, most AVRs drastically reduce their per-channel output when using all channels, and an ACD figure would give us some indication of the real-world output.
- Consider this link for those concerned about matching the impedance of their speakers: http://www.audioholics.com/education...ector-switch-1