The recording mixer always outputs a stereo stream of the mix that is sent to the studio (compressed, or lossless with the PRO version). Single channels can be switched to be recorded on the client side and then can be requested to be sent in full resolution, each creating a track in Cubase/Nuendo with that channels’ recordings (for those who might be interested).
Beeing a full fledged 16 channel mixer, it makes sense that its output is stereo. However it also makes sense to assume (as you do) that edits on the “master” stereo recording track should be reflected on the individual HD tracks…it may be tricky but we’ll certainly look into this.
Meanwhile here’s how I think you should be able to convert them stereo files to mono:
select audio event in the arrange page
in the audio menu, “Find selected in pool”
right click on the selected audio file and choose “convert”
set channels to 1 and options to replace the file
Haven’t tested it but that should do the trick?