Pioneer SX-6000

[rockinnomo]

I have a Pioneer SX-6000 receiver that has selectable outputs to 3 pairs of speakers plus a single "center channel" speaker. I listed it on eBay before I was able to find what this setup was called. Now I'm getting questions about it. Anyone know what it is? eBay item #230313429599.
Harvey

 

[timbre4]

To my knowledge it would simply be just a L+R summed mono signal.

It would not be like a modern surround reciever with a discrete signal path to feed a unique input channel's output through it.