This review might explain why despite my many attempts to use my SMSL A300 as the primary amplifier, it always ended up back in the storage. There is nothing particularly wrong with it, but I never found it that great either.
I would stick with Aiyima A07 in your case. The difference is marginal, and Fosi will probably need to be 50% on dial to achieve the same volume (due to how the volume knob is designed and a different gain).
I'd rather have the slightly lower gain to achieve higher THD+N. Also, I don't think you can achieve the SINAD difference between Aiyima A7 (83) and Fosi V3 (88) by simply lowering the gain.
Not sure how the Amazon Japan listing looks, but in the US the Amazon listing shows the unit with black knob and does not mention the orange knob at all, so there is no confusion there. I do wish they include the orange knob.