From a post here:
https://forum.cockos.com/showthread.php?t=191158 post 23
Not sure if the url still works
In Reaper Options > Preferences > MIDI Devices
inputs:
KK1 should be Enabled + control
KK EXT disabled
KK DAW 1 disabled
outputs:
all KK disabled
In Reaper Options > Preferences > Control/OSC/WEB :
Control Surface Mode > ADD Mackie Control Universal
MIDI input: KK DAW 1
MIDI output: kk DAW 1
leave the surface offset at 0
and the size tweak at 9
leave the two checkboxes blank
Don't forget to APPLY before ok-ing
Re-boot Reaper
I have this in pictures somewhere from a guy on NI forum who comes here too sometimes - Aymara, many thanks to him/her
Here:
http://tinyurl.com/yd2ce4hh