Man, I'm so conflicted. First I was getting the impression that the Vali might only work with my HD 600 and was told that it hums with the M50 (Vali: 0, Magni: 1); then I read numerous accounts of the Vali working well with the X1 and was told by someone else that the Vali works well with the M50 (Vali: 1, Magni: 1); then I had someone tell me he prefers the Magni over the Vali for the HD 600 (Vali: 1, Magni: 2); then I did a thread search and saw numerous instances of praise for the HD600+Vali combo (Vali: 2, Magni: 2); and now you're telling me I should just go for the Magni due to its versatility (Vali: 2, Magni: 3). This is driving me crazy!
I'm contemplating getting the Vali and just selling whichever headphones don't work with it. Have you particularly tried the Vali with the M50 or MDR-V6? I already know the Vali works well with the HD 600 and X1, so the only uncertainties are how it pairs with the M50 and MDR-V6 (and the ATH-PRO500MK2, but those aren't so common so I won't bother asking about 'em).