I think what the OP wants is a “Solo in place” function: ie the signal coming out of LR is replaced by whatever is soloed. If nothing is soloed, you get the full LR mix. If something is soloed, the LR mix is replaced by that soloed signal. It’s useful in the studio (especially if you don’t have CR outputs,) but quite dangerous live: you can end up with a floor-tom solo in FOH mid-gig if you’re not careful.
Easiest way I can see to do it is to run LR from the Alt-Out sockets (they’re balanced,) and route the PAFL signal to them. In the PAFL settings, additive mode off, input AFL off, output AFL on, LR to PAFL on. Perhaps a softkey to clear solo could be useful too.
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