Currently Being ModeratedMay 7, 2013 3:25 PM (in response to ToneMonkey)
I'm pretty sure the output is just to control gain of the overall amp sim. This lets the master channel simulate the master stage of a tube amp. As you know cranking the master stage of a amp lets you get a hot power tube saturation that you don't get by just driving preamp tubes. I think Apple is letting us simulate the pre and power section of a amp so it works just like a real amp and not overdriving garagebands master track.