I'm happy to report that by creating a view on the server (using OPENQUERY, which makes it nice and quick) and then creating a link to it in my .accdb file did work as a rowsource for my combo-box.

Just for the record - I still prefer a .adp to a .accdb. I just don't think the overhead of the Jet engine has any real value. At least I haven't seen any in my (admittedly limited) experience.