I recently purchased an SU-9 Pro and encountered an issue with what I suspect is firmware. While being fed audio from Ubuntu 22.04 over USB the sound quality will degrade. This seems to happen every couple of weeks or so. It manifests as either drops outs or distortion that I notice as hollow voice. After some experimentation I found that if I go to the output menu and toggle from Balanced to Unbalanced to All Line Out and then back to Balanced, the problem goes away. This is a relatively new product and my hope is that SMSL will issue a firmware update that resolves the issue. On the other hand, it doesn't happen very often and the fix is trivial.