I’m still stumbling across shortcomings of the latest & greatest version of Nuendo compared to previous ones: Is there really no phase-switch any more in MixConvert 6? 
How am I supposed to create a proper Left-minus-Right mono setting for monitoring, then?
Is there a way to replace the cumbersome*) MixConvert by an older version or a 3rd-party plug-in?
*) → Downmix from 3D formats not working: My fault - or bug? - #2 by Dietz - Nuendo - Steinberg Forums