Originally Posted by: Death55I dont know about having to change the settings a lot when crank the amp though.

When changing the volume level of an amp, you need to compensate for the effects of psychoacoustics. As you turn up an amp, you'll perceive an increased amount of highs and lows which will make your amp sound like crap. By adjusting your EQ you can compensate for this.

Do a search on the Fletcher-Munson equal loudness contours...

The fact that tube amps saturate at high volume levels is a completely different thing. The saturation of the tubes influences the overall compression and timbre of the sound, not so much the general equalization.