The question of hiss is looking like a product variability or source hiss rejection issue. When I had a Mojo 2, I did try it with a 16 Ohm / 109 db/mW IEM with no discernable hiss. Sources were a OnePlus 9 pro and a Shanling M6, no hiss at all with either. Is the hiss coming from the Mojo 2 or is the hiss being allowed through the Mojo 2?
When looking at product quality, we need to be realistic about what a small company can achieve. As a consulting quality engineer, I can tell you that any quality level is attainable, but how much do you want to pay for it?