This may be a stupid question, but anyway...: according to the iCA4+-manual (p. 16) a double push of the rotary knob mutes ALL outputs. But on my iCA4+ and when I'm playing music/sound on my PC from Foobar2000 or Youtube (etc.) it mutes only outputs 1,2, 3 & 4, but NOT 5 & 6: I still get sound through the headphones. That's ok for me, because I thought I could also use that 'feature' in my DAW (Reaper) to have an easy 'headphones-mix' (when I use my microphone for vocals in Reaper) by double pushing the rotary knob, so my 4 speakers (on output 1,2,3 & 4) were silent and I could hear the backingtracks from Reaper through the headphones out (outputs 5 & 6) while monitoring my microphone (on input 2). But unfortunately it doesn't work that way: in Reaper - after a double push of the rotary knob - ALL the outputs are muted, so I don't hear the backingtracks and I can't monitor my microphone through the headphones.
So are there any general rules for settings in the Audio patchbay, cq. the Audio mixer for making a headphones-mix for a DAW??