I Just bought K3 ESS version for use with PS5 and when connected in UAC1.0 mode the Console does recognize the K3 and there is sound but it's so low so quiet that is just unusable and yes all volumes were on Max i tested all USB ports and tried several USB cables that work perfectly on other UAC1.0 DACS on PS5 and PS4 consoles K3 has same issue on all outputs i also tested in on PS4 Pro again same problem i guess Fiio can FIX this with a Firmware update but unfortunately they don't have firmware updates for Fiio K3

EDIT: i also tested Fiio K3 ESS on Nintendo Switch and it does works properly so the issue appears to be Only on Playstation Consoles