Thanks for answering my question~
I agree with bsfreq, but isn’t the guy’s setting in the video https://www.youtube.com/watch?v=j6gyzOjjA88&t=72s causing feedback loop as well !?
RME output 3/4 -> Compressor input
Compressor output -> RME input 5/6
Thanks to tbskoglund and I tried the video’s approach and set Ableton master output at channels 1-2 ; my connection is:
RME output 3/4 -> H9K analog input
RME analog output -> RME input 3/4
Also inserted an external audio effect plugin in a audio track, however I saw that there’s no signal in 3/4 of “Audio To” (supposed to be a signal because of RME output 3/4 ), only signal was in 1/2.(is this from software playback !?? meaning from ableton master track !??).
This time H9K seems to have higher output, but still causing feedback when raising the output gain of H9K……….