I'm looking at a block diagram of an old PA head trying to figure out if plugging into the power amp inputs (marked in red) breaks the connections from the mixer outputs to the internal amps' inputs. It looks to me that the outputs from the mixer are at the same nodes as the left and right line outputs, so I don't see what is actually being switched. What am I missing? I'm trying to figure out if I can send the mixer line outputs to a crossover and back in to the internal amps without having the unprocessed signals (no crossover) mixed with the processed signals (crossover signals). It seems that those switching jacks should work that way, but when looking at the diagram I don't see how that would happen.