OK tonight everything sounds much better again at the 8 ohm setting, thanks for that tutorial, will have to experiment with the HT passage in question again at the 8 ohm setting through the right outlet, from every indication sound will be greatly improved, i.e., certainly not noxious/distorted as it was before at the 6 ohm setting with the 663 even if not as high impact in terms of SPLs as the XPA2 was trying to be, which became moot because nullified by protect.
Very interesting how what you state may relate to dynamic peaks and the need for/benefit of headroom, and how the logarithmic nature of sound perception may give rise to the idea, "You can never have too much power," or does that idea arise mostly because most of us cannot compute how much power we would actually need to propel a given space to a given clean spl?
It seems that the dynamic peaks of HT in general require more headroom than music due to the dynamic range involved, I suppose that is more or less obvious but I still do not entirely grasp the implication in terms of how much head room I actually need/want in my setting due in part to the logarithmic distortion in perception whereby you need 10 times as much power to perceive sound that seems twice as loud (is this not approximately correct?).
BTW what's up with the power ratings with the Yamahas, the 661 is rated at 90 watts into 7 but S&V finds only 53 watts into 6? The 663 is rated at 95 watts into 7, that suggests the amp is not as powerful as I was led to believe, even in terms of backup or surround duty.
