For 5.5 it is in:
Macintosh HD>Library>Application Support>Euphonix>UserSets>MC2User>MC_USER_SET__Root
That folder hosts my Nuendo 5_5.xml
But for N6 I see it in:
Macintosh HD>Library>Application Support>Steinberg>Eucon>AppSets>Artist
I’m testing it at this moment, keep u posted.
Alan