Hello WPMU Dev Support,
WIthin Marketpress there are Product Categories.
Within WordPress there are Categories and you are able to select these Categories to be within a WordPress menu.
Quick question, can the Marketpress Product Categories be set up in a WordPress menu?
The work around I have come up with is to set up a top level widget area to drop the Product Category Widget in and use the category filter to limit it to each high level Product Category. A bit long winded but will work.