Hmm...well, one thing that immediately comes to mind is that there's too many audio paths in there. I can see what you're trying to do here, and the problem is that the case(s) itself is just outgrown. There needs to be more VCAs, submixing, utilities, and so on...the "usual suspects", in other words...but the space is simply NOT there.
One possible fix, but one that would involve the addition of a small skiff, would be to pull the Metropolix and M303 out of this build altogether and then rehouse them in a small standalone cab...a 4ms 60hp powered pod would make a good fit there, plus you'd have an extra 10 hp for a delay. Those three modules together would make for a hellacious standalone 303 "variant", especially with a built-in delay line. But the other point is that, by pulling the M303 and Metropolix, you'd then regain 60 hp in the main cab, which is plenty of space for those missing bits and pieces. Thoughts?