Asian Batman, in your previous post you said you used the 6.5x gain "once" before you changed it, and it made the bass all sloppy on your DT770s. That is not proof that SQ is 'always' better at low gain. Now you are telling me that you plugged in and used high gain with multiple sources. Which was it?
Either way, gain is not about SQ - it is about source matching and while it can affect SQ, it is not really the first place to go when summarizing an amps performance!