On a 16.0.2 there's no elegant way to send those 4 channels back to the computer.
The first 14 of the 16 sends of the 16.0.2 will only send (analog) mixer inputs 1-14 to the computer. Only with sends 15-16 you have the option to send the mixer's main mix to the computer. So that's only two channels.
What you can do is also patch a pair of auxes into a pair of inputs, say auxes 3&4 into channels 13&14. Those channels will then be sent to the computer. Not the most elegant solution but it will work.