A couple of questions to be more clear on the setup.
1. Which driver are you talking about exactly? The RME ASIO driver? Which version?
2. What do you mean with Sound applet? Which audioo driver did/could you select?
3. Could you kindly choose a more normal audio application as music player (as just a sound applet) which has also support for ASIO (RME driver) like e.g. MusicBee which support ASIO well. With the newer version (since about a year) you can playback files of different sample rates without issues. My favourite music player (I have local audio content, so I do not need a streaming application (ideally with ASIO support)).
4. Which firmware on the ADI-2 Pro FS?
5. Which audio file did you play? File type, sample rate?
6. You could also try to play RMEs shot test files (.wav) for performing the Bittest then you have at the same time an end-to-end test for lossless audio transfer. Ensure to use a suitable audio driver like RME ASIO driver or Windows WASAPI (best exclusive mode).
BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub13