Yamaha HT Receiver&Sony DVD player = No DTS

I have a Yamaha HT receiver connected via coax to a Sony DVD/SACD player. I have set the Sony player as described in the manual to output the DTS and DD tracks via the digital output. On the receiver, if I select "Auto" for the Digital/Analog DVD input, the sound defaults to the Dolby Digital track. If I deliberately set the Yamaha's input to DTS, no sound is played at all. The font panel display on the Yamaha indicates that the digital input is detected.
The Yamaha manual states that DTS sound may not be heard if the inbound digital signal has been processed by the player in any way, however I have turned off the surround processing, and set the digital signal outputs to a"raw" state according to the manual.
Has anyone encountered this behavior before? Any tips/hints/suggestions on which unit I should kick first?
Thanks all.
If the dvd has a DTS soundtrack, you will need to select DTS playback from the disc itself. All Dvds do not have DTS soundtracks and the ones that do defalt to DD over DTS.

At least mine do.

I think Dave hit the nail on the head. Go into the main menu of the DVD to select DTS.
Yeah, if the source (dvd) does not encoded DTS info, you can't get DTS sound output. Yamaha receiver detects DD or DTS automotically each time the DVD player shoots out either DD or DTS. If both formats, DD & DTS, are availabe on the DVD, the default is often DD. You need to manually select DTS on Audio setup of the disc or movie. Having selected DTS on the audio setup of the movie, your Yamaha will switch over from DD to DTS if it detects such signal shooting out from your movie. DTS is often not the default setting on the receiver b/c not all movies have DTS. I had the Yamaha RX-V1400. If I left the DD mode on the receiver, when I watch certain movie on premium cable, the Yamaha will detects either it is DD5.1 or DDPLII, if the source is only available in stereo mode. I can hit Stereo button if I get tire of DDPLII. Check with your manual again. If the manual is not clear, spend some time to play around and watch some movies to test it yourself. Good luck.