Really?? Why worry about operating temps?? You want them to run cool. My amps barely ever get noticably warm except when I am running them harder than normal. The distortion figures always seem to be lower at lower wattages so why would they be worse when run at lower levels.
Rob
Actually, Jack
is making a good point: It is not so much the temperature, per se, but that the electrical parts have been sized to be able to deal with running at high powers. Which means, that if running at light loads, that the internal structures of these parts haven't reached an equilibrium with respect to all sorts of parameters.
My suggestion when you want to do serious listening, and soon, is to thrash the system hard beforehand; driving R&R at realistic volumes, say: don't have to be in the room at the same time, of course :b! If the system is in good order, then you should be able to put on solo violin, say, and it will be sweet and true ...
DACs have this problem badly, there is a lot of capacitor coupling in some implementations, including mine, so to "condition" those capacitors I run a maximum level, high frequency, test signal through the circuitry for an hour from cold. The difference in SQ if I don't do that is quite dramatic ...
Frank