One other data point, I just did a quick test on my Android phone which can connect to either SSID, n or g. On either SSID, the DirecTV app works to stream live content. So either it's nothing to do with the SSID, which is my guess, or the Android D* app works very differently than the in-browser D* viewer on Windows in order to find and stream from a receiver and I'm making an apples & oranges comparison.
My gut feeling is that it's some kind of port forwarding requirement across the 2 access points, or UPNP is required or something like that. UPNP is not enabled on the n access point and never has been and streaming has worked fine to laptops and phones connected through the n SSID.