I haven’t an explanation, but have theorized that LDS manages the substantial buffer in the Auralic better than does Roon.
When using Roon Qobuz content is requested by the Roon player on the Core, and then multicast to Roon endpoints (like the Auralic) using RAAT as a protocol on the network.
When queuing Qobuz content using the Auralic Lightning app the Auralic Aries' built-in player software requests the content directly, so it is a much simpler process, with fewer hops, and no concern for the overall quality of the upstream hardware (since the Qobuz content is spread across servers no one knows exactly where it is coming from).
OP, it sounds like what you are looking for is an improvement in sound quality by replacing the Roon Core you are currently using (Nucleus) with a better one. As far as I am aware the best products for this job are the Antipodes line of music servers. You can purchase just the server to run Roon Core for Roon endpoints on the network, and they also offer both separate endpoint hardware (players) as well as music servers with integrated players.
Also what would help to guide you in the right direction is whether or not you are using the Roon Nucleus as a Core (server and player) connected directly to your DAC via USB, or if you are using the Nucleus as a Core with endpoint (i.e. Roon Ready) hardware built into your DAC, or with some other endpoint hardware other than the Nucleus.
