Not sure on Whole House, dont have it.
But for a 3rd DVR, they will need to run 2 more lines, and whatever the cost of the extra receiver is, they may waive the install and such fees.
It might be different, but When I got mine they had to come out and do the install, I could of, had their been the 2 lines and the switch was already their.
So If you already have the switch will multiple Coax, and have history of running lines, then thats fine. But I recommend install from them.