This is something that should be interactively available, not buried in the settings per-client.
Use case: You have a recording going on the DVR, but want to have the same thing live on another TV.
My issue is that, due to only 3 tuners, i rarely if ever don't tuner share with a cablecard channel. If it's a different source or programmng, maybe different. However, i only get to select this in the settings menu (or push setting) on the client.
I'm thinking this should be something like the Watch live/watch recording popup: if that channel is in use elsewhere, prompt for sharing.