If it were me working on a build this small, I'd never put a mult module in. You need to pack function into that 4 hp (which is too big anyway), not just a jackfield. Use inline mults instead, and pull the mult to get those hp back. And then, you can implement what Ronin's talking about with a couple of 2hp's modules...filter (of whatever type looks tasty) and their dual linear VCA so you can have those to mess with CV/modulation levels.

Better still, scrap the idea of putting this into a 3U x 104 cab and go with a 6U or perhaps even a 7U instead. That way, you'd have ample room to meaningfully expand around some of the honkin' big modules that're in this build.