In Program Mode, the Karma responds on a single MIDI Channel, which
is set in Global Mode (2.1-1a) [Menu]->[MIDI]->MIDI Channel.
+ Parameter Guide, Page 137. You must set your other keyboard to
transmit MIDI data on this same Channel (consult your owner’s manual
for the other keyboard), and then connect the MIDI output of the other
keyboard to the MIDI input of the Karma.
In Combi Mode, the same basic rule applies. You must transmit from
the other keyboard on the Global Channel if you want to play the Combis
the same way that you would from the Karma keyboard. If you want to
play separate timbres (or tracks in the Sequencer), just set the other
keyboard to a particular Channel that you want to play.
When doing either of these, you may want to make it so that changing
programs on the other keyboard does not cause the Karma to change
Programs/Combis at the same time. This is accomplished using the
“MIDI Filter” settings in Global Mode (2.1-1b). + Parameter Guide, Page
138.