Hi Pier ,
on Mac computers the commonly used “Core Audio” technology doesn´t support
Direct Monitoring. Nevertheless the following Steinberg audio interfaces
MR816 X
MR816 CSX
UR824
UR44
UR28M
update: and the Nuage I/O devices
Nio500-A8D8
Nio500-A16
Nio500-D16
bypass that limitation and provide / support Direct Monitoring on Mac computers.
As I see you are using an RME FF800 - in a simple setup you could route the
relevant input to the needed output via TotalMix manually, but of course this
isn´t as elegant as the “automatic” Direct Monitoring functionality.
I hope that info helps to clarify the situation, kind regards, Tino