I'm not sure about that particular model. But I would say 90% of tv's will NOT passthrough 5.1 audio, only 2 channel. The optical out port will generally only output 5.1 from the internal ATSC or QAM tuner, not other devices connected to it.
According to what you posted, that says nothing about whether or not it will passthrough 5.1 audio. As far as Dolby vs PCM, PCM is uncompressed, meaning it's the best sound you can get. However, optical can only support 2 channel PCM, so you will never get 5.1 PCM from an optical cable. Dolby can do 5.1 over optical, but again, we don't know whether or not that model can passthrough, or if it will just output 5.1 from the internal tuner.
Both Digital Coax and Digital optical support PCM up to 5.1, Dolby Digital up to 5.1, and DTS up to 5.1! Is does not support 7.1 or HD audio formats such as Dolby TrueHD or DTS-Master Audio. As far as the Sony R550A goes it does support DD5.1 out from HDMI connections but not DTS, make sure that your devices are setup to output a bitstream signal as most are defaulted to PCM!