I believe the header pipes are the Bassani Power Curve 2-into-2 exhaust. They have that "doughnut' pipe on the rear cylinder. There's an article on them in the September issue of Hot Bike ("Hi-Po Bagger Exhaust", p198). There's a short explanation in the article about the advantage of these pipes vs. stock.
I believe you can run any slip-on muffler (or drag pipe) on them.