Would replacing the 12AX7 phase inverter really make that much of a difference in my amp? If it does, is it something I would hear more, or feel more? Knowing the different gain factors for the 12A*7 series, which one(s) would you recomend trying first where I'd notice something? I think I have the gamut of low gain 12AU7's through a few different brands of high gain 12AX7's laying around, and even have a 12DW7 in the stash somewhere. I know someone will say to try them all, but I was wondering what some of you guys settled on and why? And what technically is going on here that the different gain levels have an effect on (in layman's terms, please)?