SOUND ON SOUND

[Arpangel]

I had a friend who used to do this sort of thing a lot, he just used a mixer that had enough group outputs, just feed those into as many active speakers, or amplifiers as you need, personally I’d go for the mixer and active speakers, far less hassle, I could do this on my little Allen & Heath, four group outs, and L-R main, although no surround panning.
I have an 8 channel panning box, that does complete eight speaker surround panning, but it’s custom made, and difficult to replicate, although smaller systems shouldn’t be that difficult to find,

[blinddrew]

I wonder if the .1 channel has any filtering built in?

It wouldn't matter - I'm suggesting using surround panning to the full-range speakers.

Ah, gotcha, I thought you were suggesting it as a cheap source of multi-channel amplification.
Your idea is better!