The final PQ depends on the source broadcast regardless of the provider.
Some channels are 720p some are 1080i some are 480i/p (basically standard def digital broadcast )
Fox , ABC and ESPN broadcast in 720p. CBS, ABC, HBO ,Discovery ,Nat Geo,History and most other premium channels broadcast in 1080i/p
Smaller networks and local stations and affiliates can vary from 480i/p all the way up to 1080i They can also vary by time of day.
PPV movies are usually 1080i/p there are times when a show is std def and commercials are HD .Format can also depend on the shows origional or archived format even though the channel is an HD channel. especially with older program episodes .
Some older Movies can usually do well if re-scanned into HD by the broadcaster as film can often exceed HD resolutions .
Maybe you can try HDMI from STB direct to TV. I would by try to by pass the receiver and use coax or toslink audio from tv to receiver .Personally I would not run video through a receiver too many things in the signal path can muddy the waters if you will a some receivers have crappy video scalers. The less #of
scalers in signal path is always better IMO just let your STB or TV do the video scaling try that out .
. I belive Dish re broadcasts the HD signal as received ? maybe someone who works for Dish or may know can elaborate.
OTOH there may or may not be signal compression differences from Dish to DTV another question maybe some one can answer
PQ in my Dish service bird no's 110/119/129 western arc is fine on LCD and Plasma there is PQ variance on the HD channels
that I would attribute to the originating channel format and the programs original or archived format,
If you have a 1080i/p TV you can set the STB output to 1080i ,if you have a 720p set try both and see which looks better depending on the quality of the scaler in your STB vs the one in the TV .I Use the HD channel menu in the STB to filter out STD def channels . . Even though the STB is 1080i or 720p output to your TV the original source channel that dish receives can make a difference .EX when 480i/p origional signal is up scaled to 1080i/720p it still isn't going to display HD. Same would apply to Direct TV. I believe Dish has more HD channels than DTV I have 200+ channels on Dish but only about 100 or 110 are HD .