loaded 6.0c - old surround projects (done version 5, 6a & 6b) now only come out L+R through sound card (emu 1820m) though Vegas Mixer shows all channels playing.
New projects, surround works fine with same Vegas and sound card settings....
Prefs are fine - it is just older surround projects - Vegas 100 percent things it's outputting surround but it never hits the Emu card. Only L+R does. But close old project, create new project and everything is fine.
Did you double check the actually routing at the master bus for each pair?
There have been cases where old project don't correctly update the actual routing of the master buses pairs.
The prefs settings are the "defaults" for new projects. They don't change an existing project routing. A project loaded can actually use different hardware routes.