Don't know that I can answer your questions, but here is what I know. I have a Samsung 47D8000 in our Master bedroom (17X14). I have a Scientific Atlanta DVR HD cable box. The sound from the TV speakers left a lot to be desired. I researched a lot and bought a ZVOX 555. The cable box has a setting for DD or other. I have it set to DD. The TV when using the TV speakers has a setting for PCM or DD. When I selected external speakers, the TV defaults to PCM. DD is greyed out so not selectable. The ZVOX is connected to the TV with a toslink optical cable. The cable box and Sony BR 5100 player are connected with HDMI cables. To me the ZVOX is a tremendous improvement over the TV speakers. It has a much fuller sound. I put a Lord of the Rings BR disk in when I set it up and the sounds were really cool. As I switched through the 3 surround modes, I could tell a difference. Stuff like water dripping in the background, wind blowing, etc. Regular TV programming and football/basketball games sound great to me in respect to announcers, crowd sounds, referees speaking, etc. I am very pleased with the results overall. Now with this being said, I also fully realize that it is a soundbase. The speakers are in a 28 inch line under the TV stand. I don't expect to hear sound coming from the sides of the room and from the back of the room. It is simply NOT a 5.1 surround system. I find it strange that people hook up a bar at the TV and expect all this sound coming from all directions thing. It just ain't gonna happen.
Like I said..............it is what it is, and I am very happy with the ZVOX 555.
BTW, I have the full 5.1 system in the great room. (actually it's a Denon AVR 2112Ci 7.1 system that has everything in place except I don't have two of the back four speakers hooked up. Wires are there, but no speakers. 5.1 sounds awesome enough).
Hope this helps.