bluorion,
Yamaha integrated amplifiers have a little bit of a different approach to "loudness button". It is not even a button and it is variable. From what I understand, and that is very questionable, it does not boost some frequencies but lowers some others. You turn it up or down as you see fit, not just on/off, so it should be helpful with atmasphere’s concern.
The only problem is that I could never figure out how not to mess it up. In my experience, it is worthless. Your experience may be better, those engineers have not put it there for nothing.
EDIT: It seems that Yamaha amplifiers you may be considering (higher-priced) do not have loudness control. There is a loudness control on lower-priced ones (model 801, etc.), but you lose meters. So you are stuck with Luxman and, maybe, Accuphase. Which is not a bad spot to be stuck at, by the way.