Combine Multichannel Mono into Stereo Mix for Edit

Hi,

I'm cutting my first feature with PP and have been assembling scenes with merged clips that have multichannel mono tracks. Most scenes have eight channels for lavs, boom, etc. To speed up the assembly, I'd like to combine all the channels in each clip into a single stereo mix, provided I can step back into it and expand the channels when I get deeper into the edit.

I thought Modify>Audio>Adaptive might be the way to accomplish this, but Adaptive is greyed out.

Is there a way I can just work with a single audio track to speed up the edit while preserving the individual channels for tweaking later?

Thanks!