I am not knowledgable what may be happening for me to perceive the LUMIN App music presentation to offer better SQ, but this opinion has shown up on other forums, for LUMIN, as well for other equipment such as WBF discussions on the very high end and expensive Taiko Extreme. I look at this similar to making a change of accessory or maybe even some equipment in your system--you note a difference and may find it preferrable to the prior configuration, but probably was not unhappy prior with the system sound. I find LUMIN App kind of like that offering me an alternative, kind of like a tweak without cost of a new accessory or piece. You make tradeoffs with music system changes.
I am not a Roon basher. I really like the convenience and music information environment Roon offers. Due to this, I use Roon the majority of the time. I too have a Lifetime Roon license. The combination of Qobuz and Roon for me has been great for finding new music, artists and tracing music and history of the involved musicians.
With Roon and Qobuz, you can add to your Library with Favorites. Those additons do show up on the LUMIN App as well. You can also browse and Discover music on Qobuz through the App. You can make your own playlists on the App that you save or you can browse and add selected albums and or songs to a playlist as well as choose when the additions will play in the order you are establishing. I have not used Spotify nor Tidal, so unable to comment on them.
Good luck on your equipment quest.
