In Windows, the input and outputs are treated as stereo pairs. If you want sound in only one channel, you need to use the panning in MiniFuse Control Center (MCC).
If you're not getting sound from output 3 and 4, you either have to :
- Click the "USB3-4" button in the "OUTPUTS 3 & 4" section
or
- Add channel strips for USB 3 & 4 - click the "+" sign on the background an select COMPUTER SOURCES 3-4
To get sound in only one channel, you must set both pan control in the "USB 3-4" channel strip to one side. Or if the app you play sounds from allow panning, you can do it there.
When using a DAW things are different, and all 4 channels can be accessed separately.