Yuppers...ALL rails need to be inside whatever safety window you choose, not just the +12 or whatever. The triple-output supplies used in Eurorack aren't capable of pulling the 'extra' from another rail that's not being used. Treat a Eurorack supply as three discrete supplies, and it makes more sense. In fact, some large-scale builders will actually use just that: three separate supplies dedicated to each rail, each one massively overspecced for the current draws found in really large systems.
OK, back to modules...we've got 7U x 84 to play with here, and the Magneto and Lo-Fi are 'givens'. Lemme screw around with this for a hot minute...
Easy-peasy. Now, this thing is set up for two discrete voices, both with the same general signal chain: Plaits + Doepfer A-111-3, so two VCOs per voice. The Quad VCA allows you to mix/amplitude control them by splitting the module by outputting from Out 2 and Out 4. Waveshaper and ring mod after that, then two Ripples to match the VCO compliment with identical VCFs. Then we have a 3xVCA and a 3xMIA for various expanded mixing/control methods. The 3xMIA also can serve as an inverter, offset source, and so on.
Next row. I put in the FH-1 I'd mentioned before as a USB host module for the Digitakt, but it can also work with other devices needing a USB host, or a computer with an adapter that allows that to connect to the FH-1. Also from Expert Sleepers is the Disting mk4, a fantastic Swiss Army Knife device, great in a small build for multifunctions. The little blue thing is a Zlob module that contains a noise source as well as the always-useful sample and hold. Then modulation sources: Batumi (4 LFOs in 10 hp) and a Quadra (4 AD or AR envelopes with looping). You know the next two, of course, and then a Mixup for a stereo out (to make proper use of the Magneto's stereo capabilities). And, oh yeah...the Row Power 40, which gives you 300 mA of extra current headroom on the +12v rail and 250 mA on the -12. A little tight for my tastes, but quite within m1sterlurk's suggested current tolerances.
The tile row is where I got artful, tho...first up is an insert module, like I'd talked about above for putting a stompbox into the signal chain, but it can also be used as an external preamp for outside signals. Then there's the neat stuff. You'll note the mixer tiles, first up...CV on left, audio on right. Now, beside those I placed the appropriate VCA, then FSRs, and last, an AR envelope.
How that works is that it gives you a force-sensor-controlled VCA for a group of summed control voltages on the left, and for the same in audio signals on the right. BUT WAIT! There's MORE...since the FSRs also output a gate, I added the AR envelopes so that you can also trigger those from the FSR's gate to send elsewhere...or even to the VCAs along with the FSRs, since the VCA tiles have dual CV inputs. This gives you an interesting control option that wasn't there before, but there was very much a hint at in the original build, and it also provides a tactile percussion interface, since you can also use the FSR/VCA/AR combo with a very short envelope and some noise, etc to tap out little noise-burst percussion bits.
And of course, your stereo output tile pair closes it out. Lots of possible patch-in for the Model-D here, plays nice with the Digitakt, and loads of sound potential in an itsy-bitsy cab. Works?