The DGX-670 has MIDI IN/OUT via the USB output, which also sends and receives audio signals since it has a built in audio interface, unlike Genos 1 ...
The problem is that the DGX-670 has no old fashioned 5 DIN MIDI IN and OUT-put ports, and that's why you would need a USB Host to MIDI IN/OUT (5 Din) converter. Yamaha tries to save money by not including the old fashioned IN and OUT-puts, sadly they also didn't include a dedicated LEFT and RIGHT Output for the DGX-670, you have to use the headphone output

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Oh well here is the link:
https://www.sweetwater.com/store/detail/...-midi-converterMaybe there are other ones out there, cheaper, I'm not sure, you can do some research, or someone else might chip in on the subject, but Kenton has good reviews.
Post Update: If the Event X accepts MIDI USB than you don't need what I suggested.