Your inquiry has received a number of good answers and really you have several options. Have DirectTV "drive the bus" and go DECA between the servers. From what you say you have, you will need a SWM switch (or dish), 2 DECA units for the DVRs and a CCK if you wish on demand access.
But I had run 4 coumputers, up to 8 DVRs and several HD receivers on a 10/100 switched network with no issues. (there is something not right with what you have) I have since gone to a full gig switched fabric, added wireless "N", and also have 3 DVRs and 2 HR receivers on DECA bridged via a CCK. (way more complex than you need but to illustrate with good components your unsupportted Whole Home should work without doing what you are seeing it do now.
Future proofing and gaining full support make the DECA option probablly the best but I don't know what kind of pricetag that conversion may net you (149-199?) You should call and ask. Try to negociate. . . You can upgrade your router and toss in a switch for 100 to 150 dollars that would fix things in your current installation. (possibly less but too cheap and you are back where you are) All things being equal the DECA conversion is the path of least resistance long term and offers support.
But on reasonable quality 10/100 equipment you shouldn't see what you are seeing. Just adding a switch and connecting the DVRs up on that might "fix" what you are seeing but it shouldn't be doing that at all. Perhaps your router has a hub instead of a switch?
Don "remember to wax the string and pull taut" Bolton
I currently have an HR21 and HR22 connected in the unsupported mode going through my router. I have problems browsing the internet when streaming HD from the other box. Do these devices need to see the internet to work? I have an additional router and was thinking of putting them on another network to eliminate the bandwith hog that streaming HD is, but would like to eliminate them from my cable modem altoghether.