Can I hook a midi controller keyboard up to the MX49 via USB rather than the midi cable?

The short answer is no.
The explanation is: this is not how it works. The USB "To Host" port on the MX49 should be connected to a qualified 'Host' device - that should be either a Windows or Macintosh computer or an iOS (iPhone/iPad) device.

The USB "To Device" port is used to connect your MX49 to a storage device, like a USB stick, for backing up and loading data, or streaming playback of a .MID file or .WAV file stored on the USB drive.

If you want to connect MIDI to the MX49 sans a computer, that means you want to connect via standard 5-pin MIDI connection; then the other device should have a 5-pin port as well.

Thanks for the fast response!

There was a paragraph in the manual that had me confused;

Connecting an external
MIDI instrument
With a standard MIDI cable
(available separately), you
can connect an external MIDI instrument, and transmit
MIDI data between the MX
49/MX61 and the connected
instrument.
Either the MIDI connectors or the USB [TO HOST]
terminal can be used for MIDI data transmission/
reception; however, they cannot be used at the same
time.Select the desired connector for use in the “MIDI IN/
OUT” parameter of the [UTILITY]
“02:MIDI” display. As
you work through the explanations in this chapter, set
“MIDI IN/OUT” to “MIDI” since MIDI is used as the
example connection here.

I see now this just means that I have to pick between using a MIDI keyboard and using the laptop, so...

Let's say I want to plug a MIDI keyboard in to the MX49 via the MIDI cable; Can I still use the USB's audio connection? Like if I want to play sounds from the computer through the MX49's line out?

Let's say I want to plug a MIDI keyboard in to the MX49 via the MIDI cable; Can I still use the USB's audio connection? Like if I want to play sounds from the computer through the MX49's line out?

If you want to use the MX49 as your audio interface, this means you connect it to a computer via the USB "To Host" port... it can also act as a MIDI interface for your external keyboard.

That means you can use the external MIDI keyboard in the DAW software. The computer will identify your MX49 as "Yamaha MX49/MX61-1" (Port 1), and it will identify your external MIDI keyboard as "Yamaha MX49/MX61-3" (Port 3).

Go to DEVICES > DEVICE SETUP > MIDI > MIDI PORT SETUP > In the column labeled "In All MIDI Inputs" place a mark next to the MX's PORT 1 and PORT 3. This will allow each of these PORTS to act as inputs to MIDI Tracks you create in Cubase. Make sure these are the only PORTS selected in that column (very important).

You can then use either keyboard (by selecting it specifically as the MIDI IN), or both keyboars (when you select "All MIDI Inputs") as MIDI INPUT to Cubase. You can use either keyboard or both to trigger any VST Instruments you may have installed. And since the MX49 is your audio interface and is connected to your Monitor Speakers, all the audio for the computer will be routed through the MX49's Main L&R outputs.

Make sense?

Perfect sense.

Thanks Bad Mister.

Not just for the forum advise, either. Your videos were a great resource when picking a board (after narrowing the brand down by comparing voice sets at a retailer). I was saving up for a MOXF, or a used MOX but after a few of your demo's I realized that the MX does everything I need when plugged in to a laptop. So you saved me a hard-earned grand...