Case is almost full and am thinking would like one of the last 2 8hp slots in the rack to add a second mixer. Perhaps something that doubles as an attenuverter. Had eyes on the Erogenous Tones Levit8, but can't quite squeeze it in.
+1 on Jim's comment. Put that M32 back in its case and on its own power, and use the resulting 60 hp hole to add modules that don't have a case and don't have their own power supply. You could also jettison the mults (use inline ones or stackcables) and you really don't have any need here for...TWO buffered mults? Anyway, you don't have enough CV destinations that require regeneration to keep the tuning stable over several VCOs (that you don't have here).
There's also a lurking problem in this...and that's an attempt to do another "modular drum machine" via the Blk Noir. However, you don't exactly have a proper trig/gate sequencer in here to set up patterns on. With the lack of that, the expense of the Blk Noir really becomes questionable...and becomes even more questionable when you've got a situation where you can get TWO machines (I'm thinking the RD-8 mkii and RD-9) for less than that one Endorphin. Then all you need is a clock pulse off of the modular to drive the machines, and you wind up with a far superior percussion complement controlled by interfaces that are intended for drum machines. And frankly, if you want a CR-68/78 sound, Delptronics makes their LDB-2 module pair, which is also based around that electro-style sound. With their version of the same idea, you wind up with a cost of only $320 and both the "voice" and "control" module together only take up 12 hp.
There seems to be this misapprehension that big and costly = the perfect solution. Nuh-uh. What "big" gets you is a lack of space in smaller builds, and "costly" just sneaks into your wallet and makes you pay twice as much for the "sexy" modules when they're not actually the best solution.
How do the dual knobs work? Do they push in / pull out to switch which channel you're interacting with?
They are concentric knobs, with the center one controlling one channel and the outer "ring" controlling another. You can't push them in but they don't protrude that far from the panel tbh. I find them ingenious and love how they save space without compromising playability.