you don't need an amplifier. you mentioned the diplexers behind your receiver, how many diplexers do you have behind the receiver? having more than one would cause the system to not function correctly. correct hookup would have: at the receiver, single side of diplexer to wall, sat side to seperator, UHF/VHF to Home Distribution; at cable junction, single side to receiver location, sat side to satellite feed, UHF/VHF to garage. once that is set up correctly, at your receiver go to modulator setup (menu,6,1,5) and check what channel TV2 is set to. if necessary you can switch between cable and OTA at this point. set the TV in the garage to the same channel and see if you're still having problems. up to ~400ft you can still get decent picture, but over 300ft you start to lose quality. post back if you still have problems