If your PS3 is set to PCM, then the decoding from Dolby Digital or DTS to PCM is done within the PS3. The AVR will show PCM. It CANNOT show Dolby or DTS, since it cannot know what the PCM was created from.
So if you're saying you were seeing DD or Dolby TrueHD on the AVR with your 5.1 setup, either you're recalling incorrectly, or your PS3 was set to bitstream at that time. (please, no insult intended, just stating facts
The PLIIx is the indication that Dolby Pro Logic IIx is active, which takes a stereo or 5.1 source and creates a 7.1 signal (see p. 123 of your manual).
For DTS movie, it is possible that the PS3 does not decode DTS and sends the bitstream to the AVR.
So, in conclusion, everything sounds normal according to your settings.
Hope this helps...