IT IS in the ‘Install device’ button list, at least on 6.5.4. There are even three Motif Rack related items : check again…
Otherwise, and in the case that ‘Yamaha MOTIF-RACK (Yamaha)’ / ‘Yamaha MOTIF-RACK ES (Yamaha)’ / ‘Yamaha MOTIF-RACK XS (Yamaha)’ are all truely missing, and that you can’t retrieve your previous device definition file, you are either for :
- choosing one as close as it and edit it as needed,
or
- defining a new one : a tedious task but doable. Choose ‘Define new…’ in the list, set the correct parameters in the ‘Create new MIDI device…’ window and use the ‘Device’ and ‘Patch banks’ panes to set everything as you have it on your gear. In the ‘Patch banks’ one, don’t forget to tick on the ‘Enable edit’ box.