Take a look in general section, there is a thread about this ongoing problem.
Nuendo supports zillion types of metadata, that most of us never use, but not channel names.
Fredo suggested splitting poly files in Wave Agent, but AFAIK this will not work. Nuendo can’t read channel names, whether from poly or split mono files. It is still the same metadata. Maybe there is an app that will copy channel name into another metadata column that Nuendo can read, but I don’t know any.