4 DI boxes after a split y cable with a still exposed other end would be a lot of money and not a total solution.
I believe that the balanced issue can’t be resolved. Not in software, and doing it in hardware is economically unfeasable. As you had mentioned, flipping the phase of one of the sides would only work if it was only panned hard center, any kind of panning automation or modulation would mess everything up.
It seems my original idea of “mono mode” being an automatic hard pan of everything that’s not fx (so browser, library, sound pool and tracks) to the left channel (or right), leaving the other one empty. It seems that for CV you can set a specific cv channel to be grounded so I wonder if that was possible in the A4 MKI when the CV outputs were combined, and if so, if a similar thing could be done here. Have one of the sides as the voice output, one as “grounded” and then no panning would be required, everything would just come out the left.
I had mentioned earlier that panning the tracks themselves is only part of the solution since if I do that, the sound browser, manager, sound pool and sound locking is all panned center by default so I still don’t hear the auditioned sound or it’s quiet or partially phase cancelled.
edit: actually flipping the phase COULD work in software if you told the tracks to ignore panning information (automation, plocks, modulation) and then flipped the phase.