I’ve never worked with DVD-9, or replication shops for that matter, but I may know the answer.
What the replicator calls a cell may be a GOP that starts with an i-frame. Vegas lets you create an MPEG file with markers at any frame.
I am pretty sure that your Layer Break also has to be at an i-frame.
Just a thought. In Vegas pro there is an option to create an iframe at the marker point when rendering to an MPEG file.
Hope this helps….
Steve Mann
MannMade Digital Video
http://www.mmdv.com