I came across this blurb in May 1968 High Fidelity:
(paste full link into browser if it's split by e-mail)

The part from London, about Klemperer recording Wagner for EMI, starts at the bottom of the first 

At the top of the second page, the piece reports that "35-mm tape (is used) when separate systems 
were being used for voices and instruments."

Are there any EMI veterans on this list who can tell me more about this technique? How long was it 
used? Aside from the Klemperer Wagner opera recording, what other records were made using this 
technique? Was it ever detailed or used as a marketing hook in EMI advertising or album-notes?

Finally, do any EMI veterans have photos of the setup, showing the 35mm equipment?

-- Tom Fine