Since the Lumin features what we believe to be a better algorithm of digital volume control, please try enabling Volume Control and Leedh Processing Volume in the Lumin app settings for Lumin U1. Set Roon to convert DSD to 705.6kHz if you use U1 USB output (352.8kHz for U1 MINI USB output) to Terminator Plus, or 176.4kHz if you use U1 AES output.
Turn down the volume before you play it back.
You may also set the Max Volume % to protect the speakers. Example Max Volume % set to 80% with main volume set to 70 equals actual volume 70 * 80% = 56.
Both the Leedh Processing Volume and the Max Volume % features are active even when using Roon.
If you use the Lumin digital volume, you don’t need a preamp.