Abolder: There is no way to tell in your particular system other than by monitering the amp with test gear, or better yet by listening.
The efficiency of your speakers, the input output specs on the equipment being used and the recording level of the source material will all effect the point @ which the amp will switch.
Play a decent vocal recording and listen for the point @ which the vocals become less fluid/liquid sounding. If this is too loud for regular listening or if it is loud enough, then you are in like Flint.
Back off from this volume a tad and you should have the best sound overall (granted that you like the sound of the Class "A" output). The different running classes are very apparent on my older MF "X" amp in the midrange, but not so much @ the frequency extremes. Be aware that CD's/LP's with higher/lower ouput will change this setting as will music that is more demanding of the amplifier.
Anyway, when I used to set the volume this way, I was not aware of the amp switching for louder passages in the music (which it was most likely doing all the time). Guess I listen mainly to the midrange when relaxing and enjoying music.
