I don’t wish to disagree with Grim at all, except that it’s not that complicated to record a VST Synth within Cubase, and it does give you a bit of an introduction to the different types of useful track that are available. So here goes… (if you want to try this, get a nice cup of tea and make sure you’re sitting down - it takes a lot longer to describe than it takes to do).
With a VST Instrument playing back, you’d kinda expect to be able to create an audio track and play the VST Instrument into that track to record it, but you’ve found it can’t actually be done directly (yet!), hence the very good suggestion to export it as an audio mixdown which is then imported back into the project as an audio track.
But in fact there is just one bit of piping necessary to do this within the project, and they’re so useful that I’m going to talk about them - Group Tracks! There I said it.
These are often used as a sub-group of audio tracks all sub-mixed through the same track so they can be processed and level controlled as one source, which in itself is staggeringly useful. But in fact the inputs and outputs (so it does all come down to that - you knew it!) are much more flexible and make Group tracks into very useful audio routing tools.
So to recap you’ve got your MIDI track playing back already - now just recklessly add an Audio track and a Group track to your project! Now to connect them all together…
Find the track in the project window that the synth (Monolog?) output plays through - the one that indicates audio level when you play. It’ll be labelled Monolog, in the VST Instruments folder. Now look in the top panel of its Inspector, and you’ll see the routing options for its output, probably set to something like Stereo Out. You can click on that and send it instead to the input of your new Group channel - Group 1, if you haven’t changed its name. Do that! Now your synth is playing back through the Group channel on its way to the Stereo output, which gives you very little except another place where you can add effects, sends, and control the level again (don’t stop now, this hasn’t got good yet).
Then if you go to the same part of the Inspector on your Audio track, there isn’t just an output routing, there’s an input routing as well - and this can (gasp) be set to receive its input from the output of your Group track! Keeping a steady hand, choose that option, and marvel at the playback of your synth part through not one, not two, but three audio channels - the synth output channel, then the Group track, then the Audio track.
And finally you can put the Audio track into record (coz unfortunately Group tracks can’t record - yet!), start the project from the left locator in Record, and your synth will be rendered onto the Audio track (with any processing you choose to add along the way).
OK, it was a bit of a trek, but in exploring the ins and outs of Audio tracks and Group tracks, the versatility of Cubase can start to be fully realised, and it is pretty darn flexible. But surely a direct connection between Instrument track outputs and Audio inputs, or recordable Group tracks, can’t be too far off, please Steiny!