| Ask the artist how important the BG Vox are. Explain to them (or better yet, SHOW them!) what happens when you've reversed the polarity on one channel in both stereo and mono. If they can live without the BG Vox in mono, then it's kosher.
I'd also suggest trying to use a short delay on one channel to create a similar stereo spread, without as much of a disappearing act in mono. You can actually monitor in mono while you adjust the delay time and (if you have the option) modulation depth until you find the most spread with the least-flattering comb-filtering/cancellation. |