great example, for such setup, haven't seen this printer before.
About noisy gears I think I can print gear covers to hide them and reduce noice if it will happen. Gears on the image are only for example purpose. Herringbone gears are must as you said.
I think about the setup in which one motor will be geared (for the back shaft) and the second probably connected directly to the right shaft. I want to remove motors from inside of hot chamber which I will probably make some day, and hide them on the back of printer.