Yes, join the existing stream that's part of what whole house is, sharing tuners. And for cable channels most all programs are repeated not only the same day but more than once. So for instance Pawn Stars can record at the later time, as could Cold Case Files, etc.... that makes free the prime evening hours for other recordings or to watch live channels.
Adding more tuners is not as good as getting a second Hopper for various reasons, but that has been discussed if you want to do a search or read other threads on it. The problem is it should not be promoted for four rooms. If there was any assemblance of a real CSR other than DIRT, they would suggest a second hopper for four rooms. Anything over two rooms for many who post here probably would mean two hoppers but there are still many couples who don't need more than three tuners for three rooms and especially if you can make use of OTA.