ALL Blu-Ray Players output the SAME digital stream of ones-and zeros for Stereo (PCM), Dolby Digital 5.1 and DTS 5.1 via Digital Optical Output (Optical TOSLINK or SPDIF Coax). Ditto for digital audio via HDMI...which can ALSO output the Hi-Rez NON-Compressed Digital Audio formats.....which your AVR can decode. Since your AVR already decodes new Hi-Rez Digital Audio formats, there is NO DIFFERENCE between budget and high-end Blu-Ray Players...bits are bits.
FYI: OPPO is one of a very small number of Blu-Ray Players that can ALSO output the Hi-Rez NON-Compressed Digital Audio formats via the 7.1 (or 5.1) Discrete ANALOG Audio outputs DIRECT to older non-HDMI AVRs (if it has Discrete 5.1 or 7.1 inputs). That was a big selling point for me...no need to upgrade from my Pioneer VSX-1015 with it's low transient distortion due to use of Power MOSFETs....DLNA was also a plus for me, but I see that it's in your AVR.
Replacing 8-in Sub-Woofer with 10-in or preferably 12-in ACTIVE Sub-Woofer with Motion Feedback will provide a very noticeable improvement....A single channel One-Third-Octave Active Equalizer (or Behringer Parametic Equalizer) located between the AVR and the Active Sub-Woofer would be the next step to suppress the boomy room modes and boost the levels for those frequencies that need additional gain....so you can hear ALL of the notes on a Bass Guitar (or Pipe Organ, or Drum Kit, whatever).
Your Pioneer AVR only has 9 Frequency Bands in it's automated Equalizer,...so it doesn't have the resolution to control Bass Frequency region below 200 Hz. My One-Third-Octave Equalizer has TEN band controls below 200 Hz and I'm going to guess your Pioneer only has maybe FOUR (my VSX-1015 only has TWO).