I have the GP Gain Balance with one of the left out going to both output 3 and output 4 on the audio interface out. I am using quite a bit of trim attenuation (-29db) The level shown (and heard) on audio out 4 is quite a bit lower than audio out 3. This seems to go away when using no trim but from -10db to -30db master trim it is pretty severe. GP 3.50 Mac 10.12.6
I can fix it by putting a GP gain plugin inline with the output split going to audio output 4. I can even leave the gain at zero and this seems to create a buffer that prevents this issue.