I've stumbled across it in the past as well.
In the manual, I think the term "TRS" is always used when RME simply refers to the physical connection, which is then "TRS" for an "XLR/TRS" combo jack.
Then, when it comes to usage, it looks like there are only the 2 options:
- XLR as balanced input (either for microphones or as full line input).
- TS unbalanced as instrument input (Hi-Z), therefore the higher impedance
I never used inputs 9-12 for balanced connections, because I think I got an answer, that this won't work.
Only wondering why RME uses then XLR/TRS jacks, maybe XLR/TS are not so good available on the market or it was planned to offer TRS balanced as well, but was later withdrawn, only speculation, no idea.
BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14