It sounds like you've found an unusual disc - and one with a woefully inaccurate case, as clearly there is no DD or DTS data present. If I had to guess, I'd guess that it is either an MLP track (the audio format used on DVD-Audio) and the player has decoded it to multichannel PCM, or it is just an uncompressed audio track of 5.1 PCM (similar to what is provided on many Blu-ray discs). The latter would explain the lack of a menu and the lack of digital output.