^ just to add. maybe the files you're playing are all Dolby Digital encodes.
since this AVR already employs Dolby Surround for 8ch upmix, it's defaulted that way, saying, Dolby Surround. Dolby Surround (for 7.1ch AVR's) is the new replacement of Dolby Pro-Logic IIz (for 5.1ch AVR's). but as mentioned, you can change/opt for other Sound Modes.
as for my X1300W, if I play movies with:
- DTS, DTS-HD MA, it displays DTS or DTS HD MSTR, respectively
-- this can also be changed to Neural:X
- AAC Stereo, it displays Stereo
- AAC MultiChannel 5.1 - it displays Multi-In
- Dolby Digital -- it defaults to Dolby Surround but I can change it to Dolby Digital
- Dolby TrueHD, it displays Dolby TrueHD
- ATMOS, it displays ATMOS
- DTS:X, it displays DTS:X
- DTS 96/24, it displays DTS 96/24
btw, I mentioned ARC because if you use the TV's USB for movie, it can only decode/pass-through upto 5.1 channels. so even if you play a Dolby TrueHD or DTS-HD MA 7ch encodes, you will only get the core 5.1 to be passed-through. the same goes for S/PDIF. so it's best to use an NMT that could decode/pass-through 8ch to your X1200W.
=))