Let me see if i've got this right:

Osc A to Ring mod 1 X input
Osc B to Ring mod 1 Y input
Ring mod 1 output to Ring mod 2 X input
Osc B inverted to Ring mod 2 Y input

I've had a few goes and i can't tell any difference between 'mod demod' and just plain two ring mods in series, the following audio has a VCS in the patch to switch the Ring mod 2 Y input between inverted and non-inverted on each new note on.

http://homepage.ntlworld.com/marieshrewsbury/ModDemod%20101009.wav

It sounds just the same First part is using an LFO in the audio range, then i swap patch cables to use a VCO instead, but there is no change on alternate notes.