So...how would you send an inverted envelope to your Sisters VCF?
Oh, snap! No attenuverters! C'mon guys...also, I would suggest some more VCAs be added, since this thing's got ample modulation sources but there's only four VCAs in evidence that can be used for either the audio OR the modulation/CV level control.
Now, while it might be possible to take this to a two-voice paraphonic system in a space of 2 x 84, this would work loads better in a 2 x 104. Something like a Mantis might be a better pick here. With the extra space, also, you can easily add some attenuverters, a bit of logic to screw with your timing, and make two PROPER voices with two VCOs each, their own VCFs and VCAs, summing down to a proper stereo mixer. And if you were to go with an Intellijel 7U x 104, you'd then have the tile row for some of your basic functions, such as audio I/O, MIDI interfacing, etc. That's what I would recommend, tbh.