Hope I'm not to late to help but here goes. If I were to go to a house with the problem you describe the first thing I would do is find out if the PC side of the dish is an independant feed (because I have never had to install that style dish before). Based on what you have written it sounds like it is. Second, swap the physical locations of the two receivers. If the problem follows the sony than you can rule out the wiring and the LNB. If the problem stays, leave the receivers in their swapped locations and goto the dish, undo the LNB and swap the two feeds. If the problem switched to the other receiver again the LNB should be replaced. If the problem is still in the same place, (on the phillips receiver which is still in the sony's original location) than the LNB is still good and the line and hardware between the dish and receiver is the culprit. I think it is very likely that the inline amp is a problem. I have seen many of these fail regularly. Try taking this out and replacing with a regular barrel connector. I have many installs with upto 200'-250' of line with no need for an amp so I question wether you really need it or not. Also, is it located at the receiver or the LNB? Location placement can make a very big difference on the strength of the signal that the receiver is receiving and several of the transponders are very sensitive to that level.

Hope this was insiteful.

By the way, I would not be surprised to find out that you have a bad sony receiver. I have seen them go bad often and some have done some really bizarre things. (Especially with the 55 and 65 series).