ok, I've been jamming here at home and think I found a solution
The practice place in question has this slanted Marshall cab that surely has the dreaded t75s. Years ago, I played through better cabs and had similar issues, but right now that bright cab is a glaring concern.
I was flipping around and realized the Tills Recto would stand a much better chance. The Butterslax has those modern highs (kind of Fortin-ish in its attack which are usually awesome but just aren't translating well for this cab.
The Tills Recto is much thicker and smoother on the highs. I'll try that next week.
Should I have that Gate in the x slot? Right now I've had it in D as that's where I saw it on a modern metal profile somewhere. In tube amps, it would be the x slot. I may try that to see what happens.