I did some A B comparison test between Hifiberry DAC+ DSP running HiFiBerryOS and my Yamaha RX-V585.
- Spotify Connect > Hifiberry DAC+ DSP (DSP and EQ Off) > Optical Out > Yamaha RX-V585 (DSP Off)
- Spotify Connect > Yamaha EX-V585 (DSP Off)
What I hear is that the Yamaha play its spotify audio less muddy, less distorted more bright. It's almost comparable to Tidal CD quality > Roon > HiFiBerry.
How can this possible? Is the HiFiBerry DAC involved even with optical output? Could be that the Yamaha is upsampling the audio from its Spotify Connect?