Building on that, make sure all the coax is rated for sat. service (swept to 3GHz). Some RG-6 will meet this requirement. RG-59 is not adequate. If you have RG-6 installed to all locations you're probably good to go even if you're not sure about the frequency capability as long as the runs are relatively short. (This is saying that even if the RG-6 is not rated to 3GHz it will likely work over shorter runs.) 3GHz rated coax is needed at least for the cables running from your central point to the dish location. I will also be needed from the central point to the rooms where the DVRs will be located if they are not at the central point.
Where are you planning to locate the DVRs? I assume you're getting 2 625s. In a basic setup they need to be in line of sight for the "nearby" TV locations (TV1) as the remotes for TV1 for each receiver are only IR. (The remotes for TV2 are UHF. See the brochure link below.) You could come up with IR repeaters for both TV1 remotes if you need to locate the DVRs completely out of sight. That might allow you to locate both receivers at your central box, then feed RF signals to the 4 rooms where you want TVs through the existing coax cables. (Those then would not need to be 3GHz rated.) But this will not give you the best TV quality for the rooms that could be connected to the "nearby TVs" (TV1 outputs). For those you would have better quality using the S-video outputs or at least the composite outputs from each receiver, assuming your TVs have those inputs.
If I were you, I would choose 2 primary locations where the DVRs would be close to the TV and could "see" the IR remotes. You then would run another coax to the second room to be attached to each DVR, from the TV2 coax output of the DVR to that room. You could do that by back-feeding the TV2 signal through the same coax that provides the sat. signal to the DVR by using a diplexer, then in the central point using another diplexer to split-off that TV2 signal again into the preexisting coax to that second room. You would do that twice, once for each DVR/second room.
http://www.dishnetwork.com/downloads/pdf/product_brochures/625_Prod_SheetWeb.pdf
EDIT: The above 2 posts hit this thread while I was typing this reply. Sorry for the duplication of information, but we all think alike here...!
Welcome to the forum, BTW...!
