If it's what MajorFubar says, enabling the sending and receiving of the knobs on the MxB, then you should run the MIDI Control Center software:
- select the device tab
- make sure that "MIDI param send" and "MIDI param receive" is set to "On"
- set "Enable 14-bit automation" to "On" if you want the highest resolution, or keep it at "Off" if 7 bits is enough
You may also need to check that your DAW is recording MIDI Control Changes, as standingwave says.