# DTS 96/24 Decoder: No
# DTS 5.1-Channel Decoder: No
# DTS 2-Channel Downmix Output: No
# Dolby Digital 5.1-Channel Decoder: No
# Digital Output (Dolby Digital, DTS (DVD), MPEG Audio, Linear PCM): Yes

this is the first time i see a NO for DVD player. the specs also didn't mention about analog L+R output terminal. if this is true, then the player cannot decode the audio internally. it only bitstream the digital audio out through SPDIF coaxial to an external AVR.

based on the picture, there's analog L+R audio out. it means that the player can internally decode DD and DTS.

if you wanna get 5.1 surround sound, make sure you go to settings page and enable the "digital out".

did you properly connect it to your AVR? can your AVR display the type of input that it detects? if yes, what does it show? should show 3/2.1 or 5.1 or sth similar.
(i'm not a pioneer AVR user)