just changed the usb-dac output from RCA to XLR, the sound is better than RCA, but even I set "HOT" = 2 or "HOT" = 3, the sound is almost the same, is it normal?
Set to "2" means Hot pin is 2, set to "3" means Hot pin is 3. It simply means there is 180 degree phase reversed between these 2 settings. Try to listen more then you will notice the difference.