This should do:
Take your existing project.
a) create an Input (Devices/VST Connections) with your TB (Talkback) Microphone as input source, name it “TB/Performer”.
b) insert the VST Connect plugin into the corresponding Input channel (not an audio channel, it has to be the Input channel). Its input is what the Performer hears (your TB Mic, along with the playback), its output is what comes from the Performer (which you want to hear and record).
c) create a group channel, label it “To Performer”. Make sure its output is routed to your main mix output (default). Insert the VST Connect Cue mix plugin here.
d) for each track that the Performer should hear, send to that group channel (just like you would send to a reverb fx channel, for instance). I prefer to use real sends here, not multi-output routing.
Whithout beeing connected, when you run Cubase, there should be activity in this “To Performer” Group channel. Once you assured that, lower the Volume of that Group channel to zero (you don’t want to hear it, only the Performer should), but do not mute it.
e) create an audio track, named “Performer Mon”, its Input source is the “TB/Performer” Input, output to main mix (default). Engage the white/yellow Monitor button (next to the record button).
Now connect. Make sure the “Talkback” button on the top left and the TB rotary knob are engaged.
You should now hear the performer via the “Performer Mon” audio track/channel. The Performer should hear you (your TB Mic is sent via the VST Connect plugin in the Input channel). When you run playback, the Performer should also hear whatever is sent to the “To Performer” Group channel.
To record the Performer, create further audio tracks with the “TB/Performer” Input, but don’t activate the monitor button there (to avoid confusing echo), just use the record buttons (Preferences/VST/Auto Monitoring should be set to “Manual”).
This may sound a bit complicated but in fact that is what you also do when you record somebody next door: provide a headphone mix (“To Performer”) of the playback and send your Talkback Mic to communicate. The one difference here is that recording and monitoring the Performer must be split (one “Performer Mon” channel with active Input Monitor, several record tracks with just record activated).
Of course, hardware i/o and connections on the Performer side should be set up correctly, you can remote control that in the Performer Setup. Also, do not mess with settings that you don’t fully understand, eventually delete preferences (/appData/roaming/Steinberg/VST Connect SE.ini).
Hope that works…if not, drop me a PM, so far we have sorted out each and every problem