I have a Voyager Electric Blue, but I’m considering downgrading to an Old School since I only ever use the ‘real panel parameters’. The recent videos of the Slim Phatty poly chain are exciting, though, and looking around a bit I haven’t been able to find a definite answer on this yet: Can the Voyager Old School be used with a Slim Phatty for the “poly” mode?
The short answer is no - the Old School has no MIDI capability, and poly mode is only available via MIDI.
Would work with your Electric Blue, though… 
- Greg
You can get Midi for the OS no?
It’s funny but I’ve seen a number of posts from folks who seem actually surprised that the OS doesn’t have MIDI.
Wasn’t that the whole point of the OS?? No digital anything including MIDI??
dml
Yes, just send it to Moog. The upgrade costs $3295. You can also get the backlight upgrade for $200 at the same time.
I had a bit of a giggle when the OS came out and the first thing peeps were asking for was “how do you sequence this thing??”
Each to their own 
[/facetiousness]
Some argue that theres no reason that it couldn’t have Midi, if only for Keyboard pitch/aftertouch/velocity, since it does share the same digital keyscanning board as the other voyagers.
May be. But most people want a Midi capability so that the Old School can be ‘played’ via external Midi based sequencer, hardware arpeggiator (such as the OB Cyclone), or otherwise manipulated via the likes of Ableton, etc. And of course, “notes” are only part of the equation. With nothing but pots wired to the analog board and no code between, the implementation would only be half-done and nothing more than what you can do with a decent Midi->CV converter.
So here is my advert for the OB SEM (modern “Tom Oberheim” version).
It’s outstanding… tracks perfectly, and has a capability to bind a Midi CC (any one) to control voltage patched into your choice of CVs. Can alternatively take either Channel Pressure or Velocity for CV2. And Portamento and Pitch Bend work perfectly.
Doepfer also makes an affordable unit. I haven’t tried it but it’s specs tend to suggest that it would work well with Moog gear: http://www.analoguehaven.com/doepfer/mcv4/ 110 Euro direct from Doepfer or $180 from Analog Haven in the states.
CV to MIDI is what I meant.
As GregAE said there is no way to poly chain the OS with neither the Voyager or the LP.
However it is possible to send the OS’s CV outs to control MIDI devices including the Voyager and LP. You’ll need some external gear such as:
http://www.paia.com/midibrn.asp
If you google CV to MIDI you’ll find more!