Is it possible for the mc6pro to send midi over usb to an ml10 and then on to a second ml10 via regular midi cable? Or will I need a midi cable from the mc6pro to the first ml10?
Yes you can, if you use the USB HOST port on the MC6 PRO.
But the better way would be to just daisy chain the 2 ML10X
for example
MC6 PRO 5 Pin MIDI OUT >> ML10X-1 5 PIN MIDI IN
ML10X-1 5 PIN MIDI THRU >> ML10X-2 5 PIN MIDI IN