Well... the A-135-2 is a yes AND no answer. It's more of a quad VCA. It'll work as a mixer... but then you give up the ability to use it as VCAs. You could press the Maths module into mixing duty if need be.

I'd go with clones of the Mutable stuff in less HP to make room for a dedicated submixer... else consider replacing something like the Intellijel sequencer with something smaller or a stand-alone sequencer. If you have your heart set on the configuration I would go for the smaller clones.

My $0.02.