can I use m3 module with an external usb/midi keyboard?

[jazzjams]

can't find this listed in manual, but would like to use with more portable keyboard like a Korg Microkey with M3 module.

[voip]

The USB A connector on the rear of the M3 module only supports memory storage devices e.g. hard drives, CD drives, or memory sticks. The M3 module cannot act as a host for external MIDI over USB devices, such as the MicroKey. It doesn't have the necessary hardware design features and code to do so. It can act as a client for MIDI over USB via the USB B port, so could be connected to a computer, which could then act as the USB MIDI host, and source of MIDI messages. Alternatively, pretty much any keyboard with MIDI outs via DIN connectors could be used, e.g. Korg Kronos, M50, M1, or a MIDI only board e.g. Korg KONTROL-49 (out of production), Roland A49. A further alternative might be the Korg Radias keybed (RD-KB), via the TO KEYBD connector on the bottom of the M3 module, and dedicated cable. And yet another alternative would be to use a USB to MIDI host module, which has MIDI DIN out, to which the MicroKey could be connected.

[HardSync]

And yet another alternative would be to use a USB to MIDI host module, which has MIDI DIN out, to which the MicroKey could be connected.

This is likely your cheapest and your best option for its sheer simplicity. There are lots of MIDI interfaces out there that will get the job done for you.