well there should be a difference, pushing channel volumes pushes the preamp tubes harder, and pushing main output, pushes the power tubes right? so there should be different blends depending what you push? i do feel the main output should be close to 3, and channel volume around 2 for a great tone with full power / simul class / triode...but my tastes for this amp change every day haha, and no matter what configuration you use, amazing tones are available