#1 - get separate cables for the Comcast Internet and your Dish. Sharing cables is a surefire entry into fingerpointing between providers.
#2 - You have to use Diplexers in PAIRS. However - I don't know what frequencies the Joey is using, so again - go back to separate cables. They may very well be using the same band. If you didn't have the Hopper / Joey setup - then your old DirecTV setup using the diplexers would have worked.
#3 - There maybe some other network technology (ethernet, wifi ?) to connect your Joey to the Hopper, and leave the coax cable for the cable modem..
#2 - You have to use Diplexers in PAIRS. However - I don't know what frequencies the Joey is using, so again - go back to separate cables. They may very well be using the same band. If you didn't have the Hopper / Joey setup - then your old DirecTV setup using the diplexers would have worked.
#3 - There maybe some other network technology (ethernet, wifi ?) to connect your Joey to the Hopper, and leave the coax cable for the cable modem..