Hello DJ,
The M3-61's keyboard is integrated with the module so that velocity curves, aftertouch curves etc can be adjusted in a straightforward way within the M3 OS. When you use the M3-M with a MIDI keyboard, you have to ensure that velocity curves and aftertouch capabilities and scaling factors are set correctly on BOTH the MIDI keyboard and on the MIDI input section of the M3-M. There are some "issues" on scaling of note and AT velocities that have to be resolved. Searching
www.karma-lab.com forums will tell you about this.
Also there is the question of integration of the ribbon controller, the 4-axis joystick, and the two programmable buttons. It is posible to do all this with external MIDI devices. But it's not easy to configure. And unless you provide these devices, some aspects of the Programs and Combis on the M3-M will not be accessible.
So, most of us who bought an M3-61 (or -73 or -88 ) did so because we wanted a ready-made complete solution that works "out of the box". Whereas those who bought the M3-M for integration with other MIDI equipment have had to do quite a lot of work to achieve the equivalent level of functionality.
If you have the experience to solve the MIDI integration issues without needing a lot of help and guidance (because it won't all be documented) then it is of course possible for you to
design yourself a very nice solution. Note the underlined emphasis on "design yourself". Don't assume you will succeed unless you've done this many times already with other complex MIDI equipment. The M3 is about as complex as it gets.
If I had taken the same decision as you, I would check which people registered as owners of an M3-M on
www.karma-lab.com. I would search their posts to find out which MIDI keyboards and external controllers they were using. I would review their musical contributions on Karma Labs forum to see which people have had the most success. I would buy the same MIDI keyboard and controllers as they are using, and I would ask them for advice on all the setup and configuration aspects.
But then again I'm lazy, so I bought an M3-73
Best regards,
Rob