Does the Whole-Home communication data go through/interact/burden/put additional data load on my home router/network?

If you use your network to connect the receivers together for WHDVR, then yes it will impact your network performance. If you use the DIrecTV DECA system to interconnect them, then WHDVR does not impact your network since all the WHDVR traffic stays on the DECA network. However, OnDemand downloads can still have an impact on your network.

Thank you for the reply. I'm no tech guy, but each receiver does have the DirecTV DECA (white box with lights on it powered by the receiver and has a network cable connected only to the receiver/DVR.  So my understanding is that I am using the DECA system. 

And I know that before these DECA's were installed I could see only the DVR's that were connected directly to my network on the computer mapping of the entire network. But now, with the DECA system every receiver/DVR shows up in my home network. Is that consistent with the DirecTV equipment being interconnected correctly through the DECA system?

Each of your receivers/DVR's still individually have a connection to your home network for the Media Share and DirecTV2PC network features that interact with your networked PC as well as an Internet connection for the On Demand for the DVR's. But the actual Whole Home DVR service(sharing content between boxes) does NOT go through your home network. As user sungam stated On Demand(as well as using Media Share or DirecTV2PC) can potentially affect your home network because they are accessing your PC or the Internet through the router when you use those particular DirecTV network features.

"When you use those particular DirecTV network features."  Does that mean only when we are watching an "on demand" program?  Or are the first bits of movies being downloaded more frequently to avoid interruptions?

And if that last bit is true, is it enough data to slow me down during normal waking hours? And I suppose there is no way to tell it to do it's downloading at 3:00 a.m.? Or is it just not enough data/load to worry about? 

And with the SWM/Whole-House system, do the On Demand shows just go to a single DVR or does it get fed to all of them? 

Not when you are "watching" an On demand, but when you are "downloading" the On Demand. On Demand "only" records on the DVR that requests it, not all of the DVR's. Do not confuse this with ordering content from the DirecTV website online or from a mobile device....I am referring to On Demand requested from the DVR On Demand menu/channels. This requests content to be downloaded to the DVR over your network's Internet connection when it is requested and no you cannot request it to download at a later time. And when you access Media Share through the DVR's "Music, Photos & More" menu selection and begin streaming content from your PC it uses the home network while doing that. And if you start up the DirecTV2PC application on your PC and begin watching content from your DVR on the PC it uses the home network while doing this. My "guess" would be that the highest demand on your network's bandwidth would be while watching HD content via DirecTV2PC, followed by downloading HD content via On Demand and the least impact would be using Media Share(that's an uneducated guess).

Depending on your ISP speed, a download can soak up 7 Mbps or so.  Why don't you just take a few minutes to set up your downloads before you do to bed?  The data is sizable.  A HD movie is 4 or 5 Gb.