I have this, the sound of metal being scraped makes me feel physically ill and s sounds in vocals can be incredibly irritating and are impossible to ignore even when not irritating
I doubt I'd be able to handle the 7506
I have these headphones and I use Oratory1990's recommended EQ for them and they sound great with it. I'm quite pleased with them because I don't listen loud and they are headphones that I can comfortably wear for hours, something that can't be said about quite a lot of others.
This imo is definitive proof that there is no point in buying a tube amplifier other than the novelty factor. What people like is the high output impedance causing a few decibels bass boost which can easily be achieved at no extra cost through EQ :)