To find out the midi ports setup of your system, please evaluate the (midi-destinations) function:
(midi-destinations)
=> ((0 . "Bus 1") (1 . "Bus 2") (2 . "Bus 3") (3 . "Bus 4")
(4 . "Bus 5") (5 . "Bus 6") (6 . "Bus 7") (7 . "Bus 8")
(8 . "Bus 9") (9 . "Bus 10") (10 . "Bus 11") (11 . "Bus 12")
(12 . "Bus 13") (13 . "Bus 14") (14 . "Bus 15") (15 . "Bus 16")
(16 . "Session 1") (17 . "Keyboard") (18 . "MIDI OUT") (19 . "UM-ONE"))
There are two possible ways to assign a port. One is with the port number and the other is with the port name (a string).
(instrument
:omn omn-form
:port 0
:channel 1
:sound 'reaktor
:program 1)
now with a string:
(instrument
:omn omn-form
:port "Bus 1"
:channel 1
:sound 'reaktor
:program 1