I deleted ALL channels under this activity. Because I almost never watch live tv anymore (excepting football season). And they channel guides for this activity would merely serve to require more mode changes from play to nav. Also if you really need to watch live tv, you can get to it from the channel guide.
the canned activity should have two menus 'Play' and 'Navigate' And a third defualt menu that lets you chage activities once you are 'Watching Pvr'
No go back to add activity, and select 'change button mapping' or whatever sounds closest. This little wizard will allow you to select what command to send to what device under what menu for what activity. Sound complicated but the web based wizard is straight forward.
After re-mapping, I'd suggest you go back and re-name all of the just created activities to something that makes sense. 'Zap - Nav'