Headphone amps, external power supplies: what difference do they make?

^^ unless something is really screwy with that amp you are not getting any coloration. That's my point, you took one good output and substituted it for another equivalent one. That doesn't do anything . Then you posted to tell us about it.

I am not offended and I didn't mean to insult you but I was trying to suggest to you that you may not understand what you are doing and might want to read a bit more.