Crazy question… Would it be possible to mod the entire current Moog line of synths for stereo inputs & outputs? I say this only because having to buy 2 of everything is just a little expensive.
There’s nothing in any of the line, aside from the Voyager that would benefit from stereo outputs. The only thing in the Voyager that warrants stereo outs are the dual filters, which are hard wired as a mono input. It would probably be possible to locate the inputs of the Parallel Low Pass Filters and fit it with 2 Inputs for stereo processing, but this would require soldering and/or adding/removing parts. As for adding stereo Out’s to a Mono synth, you would need some form of stereo processing. Dual filters is one. Panning as a modulation source, stereo chorus/delay/reverb, etc. All which can be processed externally. Really, the only synths that benefit from multiple outputs are Multitimbral Poly Synths (ie DSI Poly Evolver / Tetra).
Anyway, Stereo Inputs on the voyager as well as dedicated control of the LP cutoffs would be most excellent.
Interesting timing. I have been working on a stereo pedal idea that would be perfect for this scenario - one that adds width to the stereo field from either a mono or stereo source. I’m still wondering how much interest there is in the market for something like this.
I’m on the fence as to giving moog the idea, or making my own…
I’d really like to process external stereo sources & have them sent back in stereo. Guess it isn’t possible
Or process the left channnel, then reconnect and process the right channel.
Hey you have done a good job ,nice explained.I am not a good Moog guitar player currently leaning about it ,but after reading your answer I can easy got problem with proper solution.Thanks!!! 
Truth be told, why not get an outboard analog filter (or two?) if that’s the kind of processing you’re after. Several options out there especially used that are substantially cheaper than buying two Moog synths… If you really wanted Moog you could just buy a couple Moogerfoogers…
OTO Biscuit is a stereo analog multimode filter (different flavor than Moog though) and a whole lot more (bitcrusher, rate reducer, delay, sequencer, synth, distortion…etc).
Other than that, 2 MF-101s would suit the bill for stereo filtering.
What I do is record Moog parts twice and pan them. Costs me nothing other that a bit more time in the studio.
Although I must stress that I use a DAW and automation.
But having a stereo Phatty or Minitaur, with 4 VCOs sounds absolutely brilliant.