To elaborate on that, the reason the multi-LNB's are not interchangeable is due to the spread of the orbital slots. Directv dishes and LNBs are designed to have a 2 degree spread (99/101/103) and 9 degree spread (110/119) in the same dish. Current DISH dishes and LNBs are actually two different designs depending on which arc they have to look at - Eastern arc (77/72.7/61.5) or Western Arc (110/119/129). So without getting into the geometry part of it, if you put a 2 or 2-9 degree LNB on the end of a dish designed for 5-11 or 9-10 degrees, it's going to be off by literally tens of thousands of miles in space.