To toggle back and forth between two tuners, simply set both to record. While recording , they are in essence buffering. You can flip back and forth between the two shows, back up, fast forward, whatever. When you finish watching one or both shows, save or delete as you wish. To flip back and forth between the two shows, do it in the guide. Display the guide, highlight the show you want and select. You don't need to go to the list. If there is a way to toggle back and forth with one keystroke on the remote , I am not aware of it.
Michael