In response to the private message you sent to me by mistake instead of following up in this thread.
midigal >>> all you should have to do to be able to use the MM6 with cakewalk is to add the MM6 in the options/midi devices menu and configure it to use a Motif INS file to configure the instruments.
You must have done something similar when you originally composed with cakewalk with your old keyboard setup.
As for the MM6 requiring drivers or not, I can't say if it's class compliant or not. Easiest scenario, you plug the USB cable into your computer and Windows detects it and installs the drivers automatically. Worst case scenario you have to use Yamaha proprietary drivers to recognize the keyboard.
Either way, you don't need to use the MIDI ports at all. All modern keyboards are capable of sending and receiving MIDI signals thru the USB port alone.