If you are connecting to record Audio (and MIDI) to a computer, you should connect your powered monitors to the device acting as your audio interface.

The MOXF can act as both your Audio and MIDI interface, download and install the Yamaha Steinberg USB Driver version 1.9.10 for your computer type (Windows or Mac)... connect the main L&R Outputs of the MOXF to the Inputs of your powered Monitor. When you use the MOXF as your audio interface all sound (both the synth and the computer) will travel to the MOXF outputs on to your speakers. The MOXF is a 4-In/2-out Audio Interface. The MOXF has dual stereo outputs: USB 1/2 and USB 3/4

If you elect to use an external audio interface connect the main L&R of the MOXF to the audio interface and connect the audio interface to your powered monitor speakers.