I don't have the answer for you, but I'm in the same shape as you trying to figure out the UMC204.
In my Reaper DAW software, I can't get it to record 2 tracks simultaneously when I have cords plugged into both Input 1 and Input 2. I can hear on my headphones as I'm recording it live the items going in both inputs. However, when I play it back, I learn that the DAW software through the USB is only recognizing (and playing back) the sound that comes through Input 1.....And this happens regardless of whether the mono/stereo is pressed or depressed, either way.....So basically, it's like Input #2 is worthless.
Searching the forums and help section of my DAW, I'm not able to find an answer to this.
While it's technically for the 404HD, the signals are the same for the 204HD with just two less inputs.
@Pier: For your situation, take a look at the Monitor switch in quadrant A1 as well as the Mix knob in quadrant B2. The Mix knob controls the blend of Input1-4 with PB1-2 and the Monitor switch controls whether you are listening to the output of the Mix knob or PB3-4 only.
@Joel: Make sure you have your track set as a Stereo track and make sure you have the track inputs set to both 1 and 2. I use Reaper daily with a 404HD and XR18 so we should be able to figure this one out quickly.
Hope this helps, Ken
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