Or at the very least, switch the Shuttle Control out with a more "open-ended" MIDI module, such as Hexinverter's Mutant Brain. Smaller, too.

As for the drum modules, I'd suggest leaving them out and using a drum machine that's locked up to a clock in the modular. That way, everything stays in sync AND you save buttloads of money in the process. Also, it opens up space that you can partly use to put four exponential VCAs in front of the A-138s, which is precisely what would give you CV over mix levels.

And as for stepdown from synth to line levels, just use one of these: https://www.modulargrid.net/e/ladik-p-520-4ch-out-line Best $30 + shipping you can spend for that!