The main knob of the device will always control the volume, as it is an analogue control.
The digital volume control is done in the internal mixer of the MiniFuse, so if you bypass the mixer (using the direct monitor button), the digital volume control won't have any effect, but the big knob will still control the master volume.
So, you can have two volume control, one digital controllable from the software and an analogue controllable by the big knob
OR
Only one analogue volume control using the big knob if you use the direct monitor function.
Let me know if it's clear.
I recommand you to read the manual, as it will probably explain way better than me
Cheers!