Powering on/off amps with preamp trigger

The reason that folks like to power on and off as you have mentioned is that a a pre-amp can do some nasty stuff during warm up if it doesn't have a mute circuit and you can also experience rude noises from the preamp when its shut down. Some amps and speakers have no problem dealing with these noises, you just hear some pop's or noise, however some amps do have problems and their problems can be conveyed to and be damaging to speakers. DC offset comes to mind for some reason.

If you have a good mute circuit in your pre-amp it shouldn't make a difference so long as the mute is engaged. If it is not an 'auto' mute circuit during warm up you want to be sure its ingaged.

Tbooze, Zero volume is not mute.

I really am not familar with your pre-amp. Most pre-amps have the volume contols before the amplifing stage so the amp is always seeing the full output of the pre-amps line stage. The volume control only lowers the signal from the source coming into the pre-amp, it doesn't lower the signal from the pre-amplifiers amplifing stage.

A mute circuit typically cuts off the signal after the amplifing stage and is the best way to insure that 'no' signal passes from your pre-amp to the amp. Without a mute engaged your amp is totally exposed to warm up irregularities and shut off issues.

Hope that helps a bit.