Input 11-14 on US-1641

[Harald12]

I wonder how i can raise the volume on line input 11-14 on US-1641? Input 1-10 has a volume knob, but not input 11-14. I connect my Nordlead synth in input 11 and 12 (stereo), the mic preamp inputs 1-8 i am gonna use for drums and singing and inputs 9-10 for one of my electric guitar (stereo) effect processor outputs. I want to raise the volume because i play software synths with a MIDI mic to Axon (a guitar to MIDI controller and guitar synth) and i even control the Nordlead via MIDI. And the Nordlead sounds to low compared to the software synths on my computer and the electric guitar.