https://www.audiosciencereview.com/forum/index.php?threads/luxsin-x9-smart-stereo-dac-preamp.63563/page-22
Luxsin X9 Smart Stereo DAC & Preamp | Page 22 | Audio Science Review (ASR) Forum
Perhaps because digital audio signal goes to max. 0 dBFS?
stereo dacluxsinsmartpreampaudio