Can you tell me the generalities of how you have it set up? How are you feeding the internet signal into the system? How are you then sharing it from your STBs?
Your installer will get your system online by putting a deca that his hooked to the coax cabling and will connect it to your router via cat5. My main computer is in the same room as the router so its hooked up hard wired to the router. In 2 other rooms where the coax comes out of the wallplate I have put 2way "green labeled" splitters where one leg feeds the STB and the other goes to a DECABB1R0 deca. You can use the other decas I just like this one since it uses a smaller wallwart power adapter. You can then hook the cat5 jumper to whatever network devices you like. When you get your install, Directv is not likely to give you the extra decas Im sure you can talk your installer into making or giving you the extra coax jumpers which you will need to do this. You may already have them since you mentioned moca since they should be wired similar to cable tv. Remember you need 3 jumpers after the wallplate; one from wall plate to the input of splitter, then a jumper from each output of the splitter to the STB and deca.
Here is a link to the 2way (notice green label splitter be sure to get those): http://www.solidsign...ku=874409002404
Link for what they used to call the "broadband" deca: http://www.solidsign...Kit-(DECABB1R0)
If you search ebay use: "broadband deca" as your search. You can find them on there for under $20 each.
The major drawback to doing this other then the obvious lack of support by directv is you are adding extra LOSS to the input of the receiver. For me the pros outweigh these cons not to mention as long as the decas are working you could pull the dish and receivers and your coax network will still work for your other devices.