TonyWDA said:
The “centre” music channel, as it was originally presented, does exist on the magnetic stereo releases. I was given three discrete audio tracks— left, centre, and right— when my print was captured. It’s why the 2000 and 2010 home video releases also have discrete centre channels. Disney didn’t artificially generate that with some plug-in or standalone software, it’s always existed, and it does contain information unique to that channel; it’s not just a cheap sum of the left and right signals.

Those are the 3 original channels that were manually panned towards the speakers.
Just to be clear, those 3 channels are not L, C and R. They are 3 discrete arbitrary sound channels.
The mix would direct them to whatever speaker combination was desired.

So you could have “left” playing simultaneously on your SR and FL speakers, “center” directed to SL and “right” to C. All combinations are possible but you only have 3 discrete source channels playing at any given time.

It’s my interpretation of the system and might not be 100% correct, but hope it helps.