Hi Sonic,

as long as the selected clock (in your case most likely internal) is there, AutoSync will not select another clock source automatically. This is my understanding from reading the manual. You also got a manual, check there pls, it's documented.

Which DAW? Most likely related to your DAWs export settings. This is IMHO more a question for the forum of your DAW.
Or you have an option enabled in your monitor submix so that it sounds different.

You didn't tell, what fireface you use, whether it has FX built-in and you didn't show a picture of your monitor mix where one could try to check whether a certain setting is visible.

Best add info regarding your RME HW / setup to your signature, so that this info is automatically provided.

1. Use clock source internal, as this is your main interface, autosync is then completely out of scope
2. If you would use analog ports you would always have DA/AD conversion. The routing matrix inside of the unit works fully digital. So whatever audio signal you send out to an analog output needs a D/A conversion and if you record this with an analog input then you have an A/D conversion taking place.
3. Therefore ... use digital ports then you have no AD/DA conversion, like e.g. the ADAT port. And again, clocking is not the issue here. Your device is clock master if you set clock source to internal. And even if you would have an external clock signal as clock slave, as long as the clock signal arrives on this on that digital port, then there is no need for autosync to choose an alternative for a clock signal if there would be an alternative.