Did you investigate DirecTV as well? I'm just curious why you chose Dish Network. I have a personal history and strong dislike of Dish, which is why I ask. To put it politely, their customer service is extremely sub-par.
Anyway, not having a high def display, I've not had the opportunity to compare any of the HD offerings of either provider. However, are you getting any multi-channel audio? It could be a setting in your Dish box.
Maybe, although I cringe at the thought of your struggle if you do, you should call their tech support and find out if they even broadcast their HD with multi-channel audio or not.