The correct sequence is...
ON: first - set preamp volume to minimum or muted
second - turn on preamp
third - turn on amp
OFF: first - set preamp volume to minimum or muted
second - turn off amp
third - turn off preamp
ON: first - set preamp volume to minimum or muted
second - turn on preamp
third - turn on amp
OFF: first - set preamp volume to minimum or muted
second - turn off amp
third - turn off preamp