When the client uses Cubase AI with his Audiogram, is he able to hear audio from Cubase through the Audiogram? Is he able to have the Audiogram as the sound card for the operating system and hear playback from iTunes?
I would not expect so, but it is generally best to be connected by a wired Ethernet connection without an anti-virus/firewall filter if possible.
Definitely the Yamaha Steinberg USB, and please be sure it is an updated version for Windows 10.
The main key on your system is to verify you are sending signal via the VST Connect SE Cue Send in your Control Room.