Just one.
The D1000 comes with a DPP-Twin which, in conjunction with a DPP Separator (included with the receivers), allows both tuners to run off of one cable.
In addition, all four outputs (SD only in the case of 622) of the receivers can be routed back over that same cable via diplexers, allowing them to be distributed throughout the house - if you have the wiring set up for it (ie. central distribution box somewhere).
Doing that can cause real confusion issues with remotes, and you'll have to buy additional UHF remotes to control the receiver's TV1 channels from other rooms. Make sure all remotes are set to different remote codes.
The D1000 can be problematic in some areas of the country - where are you? Add it to your profile! (Scott, I still say that should be required.)