I beleive PCM is 2-channel in this case, Dolby is multi-channel. When Blu Ray players output their multi-channel soundtracks from the front-center-surround outputs on the back panel, that is a PCM signal, I think, but in this case I would think the PCM is 2-channel only.
You know when you're watching a prime time show, like CSI or whatever, and there is an emblem that fades in on bottom that says "broadcast in surround sound?" That is when you need to see if your TV can be set to only output 2-channel (PCM) signals from the optical connection.