Hi AD,
There could be several things but we can't be sure because you don't really spell out exactly what you are doing. But here are some tips to set you on the right path.

First, if you are using the complimentary download version of Cubase, it installs three possibilities versions AI, LE, ELEMENTS... you want to select Cubase AI. "AI" stands for Advanced Integration and is a special version for purchasers of Yamaha hardware. It is able to do Advanced external audio routing (usually only available in the top of the line version). It will let you route MIDI and audio in such a way you can treat your external hardware MOXF with the same flexibility and versatility you would a software synth (as a VSTi).

This advanced routing will let you use the "Freeze" function, and use the "EXPORT AUDIO MIXDOWN" function to render (print) your MIDI Tracks as audio, you can even process them with software Effect plug-ins.

This Advanced Integration routing is your by launching Cubase AI.

Next, you need to treat the MOXF as a 16 Part multi-timbal synth by setting it in Song Mixing or Pattern Mixing mode, if your plan is to record multiple MIDI Tracks.

You don't say, but if you are using the "MOXF6/MOXF8 Editor VST", you want to launch it as a "RACK INSTRUMENT", and create a new MIDI Track for each Part you want to use. So you could wind up with as many as 16 separate MIDI Tracks.

Once you have used 16 MIDI Tracks, you can use Cubase AI to FREEZE these tracks. Freeze is a process in Cubase where it renders a temporary audio file from your MIDI Track data, it then bundles your MIDI Tracks and mutes them. This frees up your hardware for a second set of 16 Tracks.(Later you can unfreeze those tracks if you want to edit them).

It is not clear from your post exactly what you were attempting to do. Nor do you mention the type of computer. We have several tutorials here in the SYNTHS section on setting up the MOXF for audio recording, for MIDI recording, for setting up the MOXF VST... Let us know.

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