[dglcomp]

and adding to this there was the Orchestron and other derivatives of the film sound track style optical disc systems Mattel invented with the Optigan. Notably used by Kraftwerk for their string and choir sounds, of which the choir on Uranium was later sampled into the Emulator for Blue Monday. Also interesting is that the foremost Orchestron expert who has a lot of the master tapes reckons that the Orchestron choir is probably nicked from the Mellotron.
The only real advantage it had over the 'tron was that there was no 8? second time limit although plus supposedly the optical playback system was more robust, with sounds on plastic optical disks, the disadvantage, of course, was that sounds that relied on a specific envelope as the sound progressed could not be sampled very well unlike on the 'tron. It was also very Lo-Fi and did not sound as good as the 'tron.

As for the 8 track based system that was the Birotron, I believe rick wakeman put some money into it and it had an envelope generator designed by Bob Moog. I believe wakeman got annoyed with his and set it on fire!