In trying to keep the signal in the digital domain as long as possible, I have tried to run the audio out from my MOXF8 USB into my Yamaha MG10XU USB input.  But no matter what settings I make on my MOXF8 (Ie. USB I/O settings), I cannot get MOXF8 audio / sound out of the MG10XU.  I have to revert to using the analog MOXF8 ¼ inch stereo out jacks to the MG10XU analog inputs (¼ inch jacks). 

Can I use the USB connections on the MOXF8 and MG10XU be directly connected to achieve audio output from the mixer (ie. get audio output from the mixer withOUT using the analog ¼ inch jacks)?

As you’ve probably noticed, the connector from which USB Audio is available from the MOXF is labeled “TO HOST”. The MG10XU can’t act as a host - your computer can, if it has the Yamaha Steinberg USB Driver installed on it. That’s how a DAW is able to record audio from the MOXF via USB.

The MG10XU also can receive audio via USB from your computer, on channels 9/10, using the Yamaha Steinberg USB Driver and a compatible DAW, etc. (See the Owner’s Manual and https://usa.yamaha.com/products/proaudio/mixers/mg_series_xu_model/manual_interface.html.)

So no, a direct USB connection from the MOXF to the MG10XU won’t work. I own neither product so I’m not certain of this, but even with an intermediary host a digital audio connection might not be possible - that would depend on whether the Yamaha Steinberg USB Driver can address more than one device at a time.

Yeah, that’s what I was afraid of.  Thank you for the information response!  Regards.