The Sony switch was indeed a master-slave config where one input overrode the other (at least according to all descriptions I've seen of it).

Looking at this text from Crutchfield;

The inputs must be connected to the amp remote (or power antenna) lead from at least one source to switch back and forth properly.

the same is most likely true for the PIE too. If it only needs one remote out connected and still function properly, it'll switch to those associated outputs when that remote output is active, and when not, switch back to the other outputs. Most likely the actual switching elements are relays, and they'll only allow one set outputs to be active at a time. If (which I find highly unlikely) the control inputs would indeed fight each other - just disconnect the one from the "slave" unit, and according to the description above, it'll work correctly.

/Michael