Very strange. Usually when you have something like this happening with a soundtrack, more often than not it is a change in the source or source set-up but the fact that you have tried alternate sources with the same material, indicates that if everything is defaulting to PCM, on the surface, it seems to indicate that there is an issue with the Dolby/DTS decoding chips.
For starters, I might suggest you send an E-Mail to Yamaha H.O. under "support" and explain your problem and the troubleshooting you have done so far. I have owned several pieces of Yamaha equipment for years and except for one older unit where one of the DACs failed, I have never had an issue with any of them.
Based on my experience, they will usually get back to you in a day or two to advise what you can do and if repair is required, an authorized service depot in your area.
Incidentally, if none of that works and be that as it may, I have a Yamaha RX-A2000(Aventage series) in another room that I might be willing to part with.
