Since you didn't mention that you had the cab for this, I went ahead and pushed that up to 2 x 104 hp (Mantis, etc). 84 hp was just too tight to make using the synth any fun in a lot of ways. Once I did that, the design REALLY opened up. Retaining your in-hand modules, I came up with...
OK...so what happened here? For starters, I moved the buffered mult (yes, this DOES need one!) to the left end of the "audio" row, then added a Doepfer Quad Precision VCO so that there's ample oscillators here for both audio output AND audio-range modulation. Your STO is next, then out of sheer experimentation weirdness, the next two modules are one of Noise Reap's bonkers crossmodulating dual VCOs and a Happy Nerding FM Aid, which allows thru-zero modulation behavior in addition to a lot of other crossmodulation functions. The idea there is that you'd wind up with a VERY complex little FM set without too much expense and the advantage of total user-definability. At the end of the VCOs now (of which you now have SEVEN, not counting any other "sneak" oscillator features), there's a 4-in MIX from 2 hp for summing VCOs.
Filters: Forbidden Planet is first up, then the next thing is a After Later build of a Mutable Rings, which now gives you a resonant object simulator. Then there's some REAL strangeness...a Limaflo Motomouth, which is a vocal formant filter...sort of like the Sisters that was there, but on steroids. Veils next, then I added that Cosmotronic Cosmix. Now, right below that, you'll see where I placed the Erbe-verb and the Echoz, and the reason there is that the Cosmix has an AUX send and two stereo input pairs that function nicely as FX returns. This swap now allows you to deal with your effects processing as part of the mix, instead of tinkering with wet-dry balances on feeding your mix through the effects individually. Last up in the audio row is a Happy Nerding Isolator...because it's always nice to have some transformer isolation to help with noise and crud, and to have a little "iron" in the output path that you can overdrive and saturate a bit, plus it offers you a master volume for the stereo output AND the appropriate step-down in levels.
Similarly, I went nuts on the mod/control row. Yarns first, then a Kinks to add sample-and-hold, noise, a bit of logic and waveshaping via rectification. Then a Triatt allows polarization and mixing of three channels of CV/mod signals, then the Wogglebug. The lack of really meaty LFOs prompted me to drop in a Batumi after that, which should play nice with the Maths. Added three VCAs there, which can also serve as a mixer and another polarizer. Then, for the VCFs and audio VCAs, I put in one of Doepfer's new little dual ADSRs. Last bits are the Echoz and Erbe-verb.
The changes I made actually come in at around $800 over the original build, but the amount of functionality added due to that additional space addition is pretty significant. Here's a rundown:
VCOs in the original = 3 -- VCOs in revision = 7
LFO in the original = 2 -- LFOs in revision = 4
VCAs in the original = 6 -- VCAs in revision = 7
Filtering in original = 2 -- Filtering in revision = 3
...and so on. A pretty good example of "go bigger than you think you need", actually. Also, one module in particular had to be eliminated right off, that being the Doepfer A-110-4. Given that this has a 60+ mm depth and most smaller cabs tend to top out around 50 mm or so, this didn't seem like it would work out well. So the revision is missing the quadrature function, plus the Megaslope, but the additions make up for much of this.
Seems better. Layout's definitely better, and there's some sneaky bits in there (like the Noise Reap + FM Aid possibilities) that promise loads of wild sound manipulation possibilities. Some superfluous stuff got tossed, also...such as the passive mult (it makes more sense to use in-line mults for passive splits anyway). Have a look, see what you think...