It could be that the Dish can't handle high bitrates (6600 kbps is medium-to-high for h264 encoding). Is there a way to play files off a USB stick on the Dish? If there is, it may be a good idea to try that and see if that plays. That'll tell us if the player in Dish can handle this file in the first place. If it produces pixelation as well, then we know the problem.
Limiting the bitrate will trigger full transcoding, as each frame has to be re-compressed to fit within the new bitrate, so remuxing is not possible. A wireless network should handle 6-7 Mbps, if you have a strong signal and are running an N or higher network.