Because the DP series Beyonwiz PVRs have 2 tuners you cannot watch a channel from a 3rd broadcaster while the Beyonwiz is recording from 2 different broadcasters. That would require 3 tuners.
When the Beyonwiz is using both tuners for recordings you can only watch a channel from one of the two TV networks being recorded. So if the Beyonwiz is recording both ABC2 and Ten you could only watch ABC, ABC2, ABC ME, ABC HD, ABC News, Ten, Ten HD, Eleven or One. All the channels from Seven, Nine and SBS would be greyed out, in the guide and channel list. As soon as one of the 2 recordings stops all of the channels would become available again.