Well if it's any help I have the 42" 85 and the BBE VIVA 3D sound is a huge improvement over the other "simulated surround" mode thats available.
Im not sure if the 81 model only has the "simulated surround" but I found this mode to sound very strange compared to normal stereo mode. Especially the dialouge which sounds really unclear. It reminded me of one of those bloody awfull "sound modes" found on budget stereo's. Just terrible.
The BBE VIVA on the 85 sounds as good as stereo mode but with added surround soundiness. It's pretty impressive by plasma/lcd standards. As I normally watch normal tv/sky using the tv speakers I find the BBE VIVA 3D to be well worth it. I do have a proper surround setup, but for late night viewing or basic tv it works really well. It's as good as you can get without buying a proper system.
Only you can decide if it's worth it or not by testing both tv's.
As I have sky I have no need for the freesat tuner on the 81. And the fact that you can't record withut buying a seperate recorder is another negative. In the future who knows, but I would much rather spend the extra on a proper freesat pvr when they become available.