I would try the Midi cable idea first, Connect a Midi cable from the Out to the In of the M9 you want to recieve.
(You may need two cables, out to in and in to out for it to work.)
Do a system dump from one into the other. In the Midi settings,go to "Midi Dump all ?" then press "On/off" to send it. (I've got an M5 so it may be different, but there is a typo in the manual for the M5 which says "Press Tap to send" when it should say "press On/Off" to send.)
Or If you have a Midi Interface, You could use software such as "Midi-Ox" to record a "Sysex" dump of the M9's presets, and squirt that back into the other M9.
(If you do use "Midi-Ox", you have to "Send/recieve" the data.Not just "Send" it, else it won't work. )
hth :)