You should have full power on average at about 1 o'clock position to leave reserves of gain for soft sources or soft recorded CDs.
PreAmp Gain and Impact on Amp
Question; if you increase the gain output of your preamp does this ease the workload on your amp(s)? If your preamp gain goes from 10db to 15 db then you should be able to adjust your volume control down to reach the same volume level at the listening seat. Does more gain in your preamp lessen the 'load' on your amps?