I sometimes wonder if there are any qualified and honest folks left working in Harley dealerships. The things I've heard personally, along with all the things other people have reported in forums, makes me seriously doubt it. Btw, do you have the manual for that radio? It should list all the formats the unit is compatible with. When in doubt, ignore the ignorant stuff dealerships spout and consult the manual.
Simon (DesertHog) gave you some great advice, give the folks at Iron Cross a call. When Harley and it's dealers were jerking people around on those Harmon-Kardon radios, Iron Cross was helping people get the honest answers and fixing the stuff Harley didn't/wouldn't.
Jerry