First off, over on the AVS Forum there has been a lot of discussion regarding the "softer" PQ with the new Sammy HLPs versus the HLNs. I have an HLN and I like the sharpness, but apparently a lot of folks didn't, so Samsung altered somethings to soften the PQ in their newest models.
At several of the stores I viewed HDTVs at last summer, I was told that the sharpest HD PQ was with a CRT. I agreed. But, they don't produce the color saturation of a DLP or plasma, they have the old glass screen glare problem, and, as you are probably well aware, they weigh a ton. Your Sammy is also displaying several square feet more picture. The wider you spread those SD and lesser pictures, the more obvious the shortcomings of the source.
I to had to deal with the WAF when I got a Sammy DLP last summer. No HD the first 5 months so I had to deal with the poor PQ complaints. After installing new cable and using a HTS-3600 power center, the complaints pretty much stopped, and this was with an old 2700 receiver.
With the 811, SD PQ goes from acceptable to excellent. It depends on the channel and it depends on what Dish is up to. Premium channels are generally excellent and a couple of weeks ago Dish started providing an improved SD signal so even the locals are acceptable. However my locals via OTA DTV (SD) are always better than the best Dish local PQ. Sometimes Dish local PQ can be just crap.
I use the DVI input for all viewing. I keep the HD setting on the 811 on 1080i unless I'm watching a known 720p HD source such as ESPN-HD. I have an S-Video and a composite connection from the 811 to my Sammy also. I don't see any PQ improvement when viewing with those inputs. In general, they don't look as sharp as the DVI input.
From what I've seen, Comcast cable here in metro-Denver has made PQ improvements since I dumped them almost 5 years ago. However, the improved PQ isn't consistent across their channels. The lower channels with all the locals and such is still really an analog feed and it looks it.
Be careful with the Service Menu stuff. Some folks have encounter warranty refusals when the techs discovered that the service menu had been messed with. But, everyone's situation will likely be different.