Don't understand how technically it can sound better because the fundamental problem as I see it is both stereo recordings of for an example, a piano are made on different locations on the instrument and sums badly in mono. You can't avoid the aural issues caused by combining two stereo recordings taken off different locations on the same piano.

This is why I thought it best to let the keyboard do all the summing as I have to assume the engineers "fixed" the stereo issues. Using the Mono Piano actually sounds better.

But its worth a try...