Music Unlimited and Spotify both sound good on my Marantz setup, regardless of what the PS4 was actually outputing(stereo or surround).
After contacting Spotify and a few internet searches I used THIS and set things up properly. I've had no quality issues since, although, unlike most here, my audio is stereo(2 channel) not surround(5.1 channel etc) and I use optical not HDMI.
I don't use Airplay because it downsamples everything to 16-bit/44,1kHz, which for most people is great but I like to play HD Audio 24-bit/192kHz. I agree, there is a difference, not night and day, could be hardware related.
I use PCM HDMI and use my pioneer elites EXT stereo to activate the LFE and rest of the speakers as well. Annoying to have tp switch from autothe EXT but worth the added bass. Also make sure to adjust your blueray settings so when you set your recievers on auto it will use the appropriate setting, DTS MasterHD, Dolby Plus to name a few
I really hope someone actually reads this and fixes this issue. I want to be able to play music while playing a game and don't want to have to choose between music and game sound quality. This should have been addressed in testing let alone after being out in the wild for as long as it has. Very disappointing.
I have had this no bass problem for a long time. Finally figured it out. Basically DO NOT use the optical out on the PS4, instead use the optical out on the TV and let the digital signal of the PS4 pass down the HDMI. Output on PS4 set to optical and PCM audio sent straight to a stereo audio lab dac. Sounds great
I have found this to be a issue with setup and not a Spotify issue. My system had a setting called AVC (Auto Volume Control) (my sound system) with that enabled the audio qaulity was poor only while playing Spotify from the PS4, streaming it from my Android box connected to the same setup was fine. It seems like that setting and the PS4 balancing were fighting with each other when playing music, I had the same issues streaming music from USB so I knew this was not Spotify specific. Definitely something to check on your side.