IMHO:
1) ACD numbers are not important for most people but could be for some who need it for demo or for some reason they like to listen in 5/7 Ch Stereo mode.
2) Yamaha units are likely more aggressive in their protective circuit but also likely to have a little weaker power supply than equivalent Denon and Onkyo models.
3) Yamaha units are likely more reliable base on internet hearsay, but insider like M Code apparently knows it as a matter of fact.
4) Yamaha seems to spend more $ on the amp section to maximize 2Ch performance.
5) NAD, HK (only the older models), tend to spend their budget more on the power supply for better ACD output that invariably (well except for the NADs) would result in not so impressive 1, 2Ch outputs.
6) Denon (33XX, X4000 and up models) and Anthem seems to be taking a more balanced approach, such that their 1,2 channel outputs are still almost as good as equivalent Yamaha models but do better in 5/7 channel outputs.
That means I can agree to point(s) made by 3 dB, ADTG, Billy and even M Code.