Looking at photos of sd7 I see it has the vocal slider also. But this can't be practically used during a live performance where harmonies are used on and off during singing the same verse and right hand playing is going on. I can't imagine moving the slide to 0 then finding same level it was at in an instant while trying to play and sing.
Perhaps a few assignable buttons could help, but with no visible indicator it would only be half a fix as is a foot switch and require alteration to face of panel. Not looking to add user option to alter button assignments but rather a factory reassignment.
To be clear, replacing the solid mic on off button (and eliminating that function) with the more necessary voicetron on off button with led is what is needed and doesn't involve additional space on face of instrument nor expensive design alteration.