I had a long look at this, and came up with a variation on it that seems to do a better job at sound design overall. No percussion modules...sort of...
See, the problem is that when you try and build tons of functions into a small build like this, you wind up shortchanging ALL of those functions as a result. So what I did here is to kick this back to being ONLY the synth. With a few surprises...
Top row: Voicing, obviously. The dual input preamp is at the left end, with a pair of envelope followers below this in the middle row. The single VCO was replaced by Void's Gravitational Waves, which gives you a complex oscillator plus a ring modulator. Then, to process the Gravitational Waves, I added an Intellijel uFold after the 4-in 2hp mixer, which will allow for even more complex timbral behavior out of that dual VCO. Then this can be submixed again via the dual inputs on the Ripples VCF, making it possible to combine both the wavefolded AND clean outputs. After that, an Elements clone from Antumbra...which is the "sort of". Since you can use all sorts of physical models as "activators", and since you have mallet models for this, the Atom can then give you two channels of all sorts of bonks and thumps, PLUS it gets its own stereo VCF (Bastl's wild new dual-peak stereo VCF, the Ikarie). But if you want even MORE bonks and thumps, I put in a Make Noise LxD after the Mordax, so you can process its outputs through those lowpass gates.
Middle row: Mostly modulation. First are the envelope followers for your input channels, which allow you to extract dynamics from inputted signals and then output them as modulation CVs. Links, then a Doepfer noise/sample and hold module as both of those things were missing from the original version. I also put in a dual slew limiter in 4 hp (Ladik) which doubles the job of the Joranalogue while halving the space! Plus, you get selectable slewing for CV up-motion, down-motion, or all motion. Then the Clep, Stages, Maths, and Shades...followed by a Happy Nerding 3xVCA to give you some dedicated VCAs for modulation use. After this, a Quadrax/Qx setup gives you four loopable 2-stage (or 3-stage, depending on the control input and mode settings) envelopes.
Bottom row: Control. The little white thing is a Konstant Labs PWRchekr, which lets you have visual feedback on your DC rails. Then the MIDI interface was replaced with Expert Sleepers FH-1, which can work as an interface for the DAW's MIDI, or you can just as easily connect any class-compliant USB MIDI controller to this. Tempi got added because it has some special interconnectivity with the Rene, allowing you to be able to toss much of the previous clock gen/modifiers as a result. After that, I put in a mono-in, stereo-out digital effect specifically set up to work with the AUX setup on the Toppobrillo Stereomix2. That mixer gives you VCA control over levels, autopanning, VCA over AUX sends, mutes per channel, a CUE bus, headphones, and a full AUX setup with a mono main send and stereo return. I then kept the Befaco OUT as it not only has your ganged stereo output control, but it also makes the switch from CUE to output a tad easier if you patch the Stereomix's CUE out to the CUE in on the Befaco.
So...uh...where are all the VCAs for the audio? In the mixer, that's where. Also, everything was rearranged for ergonomics, especially the move of all of the hands-on controller stuff to the bottom row. And where's the power supplies? They're in the rack itself, as I opted to rework this for a powered cab such as the Doepfer LC9 or, better still, one of Case From Lake's portable 3 x 84 cabs. If you can go with an INTERNAL supply, you do three things...
1) You open up 12 hp of space
2) You can get a beefier supply than the uZeus
3) You avoid having power circuitry anywhere near the audio path, which is something you definitely DON'T want! Not to mention, those little uZeuses can get HOT, and internals can be overspecced to the point where they don't do that. The Doepfer LCs have their hefty, toroid-equipped ones, and Case From Lake is pretty much the Burger King of Eurorack cabs: special orders don't upset 'em, so you can have it YOUR way!
Now, one thing that made this rework kind of...ah...dicey was the size. A really good sound design rig needs quite a bit more of that, which again gets back to Case From Lake and their ability to resize from their basic designs. Instead of 84 hp for a width, you could go to 3 x 104...or even 3 x 120 or 3 x 126! They do that. If this build were allowed to sprawl out more, it would then have the space to be taken up to a serious sound-design level. This build is good...but if more space could make it BETTER, well...