My feet are a just a little wide according to that foot-measuring gizmo, but I have a "high instep" and the best solution I've found for that is to buy wide shoes. (Just bought a pair of Keen shoes a few weeks ago. They're butt-ugly, but *so* comfortable.)
Salomon (whose boots are generally a little on the narrow side) offers two models of snowboard boots in wide sizes. According to their website, Synapse Wide is a stiffer general-purpose boot and Dialogue Wide is softer, more freestyle-oriented. I just bought a pair of Synapse Wides last night. Fit pretty nice in the store. I special-ordered two sizes through a local store (Ann Arbor, MI) and picked between. In general, nobody around here carries Salomon boots these days, especially not things like wide sizes. Depending on where you are, you might have to special order too. I saw Salomon wides on some of the major online sites.
This is my first venture into specifically wide snowboard boots. I'll report back once the riding season starts for me. (I also bought Flow bindings late last season and only rode in them a couple days. I'm trying to solve (prevent for this season) some foot pain problems I had last year.)