Helps a lot, thank you!
I saw your comment earlier about the synergy between the Fuze and X2, and thought it might be the surprisingly low output impedance of the Fuze that caused the "magic" (especially since many X2 owners also praise the O2 and Magni, low impedance amps as well). That's why I thought that the NX1, with its less than1 ohm might be perfect.
But your preference of tube amps totally contradicts my theory, as they usually have quite high impedance, if I'm not mistaken.
Are you saying you hear similar sound from your tube amp and the Fuze, using X2s? If so, that's quite extraordinary. Would almost make me believe that you have some eq enabled on the Fuze that you forgot about?
My Fuse is also Rockboxed, and I get lost in all the options every time I start to tweak!