@soix I think you have this figured out yourself already, but getting advice on anything audio from Jason Bourne is like getting advice on the virtues of Christianity from a Taliban 😂😂
For a i2s HDMI cable I would recommend one of the discontinued previous generation HDMI cables from Audioquest. Music Direct has them occasionally at deep discount. I got a pair of Vodka for my Esoteric SACD transport a few months back at less than half of. Previous generation non-48 which still good for Audio purposes.
I used to own the Singxer Su-1 several years ago. I recall the best thing I did with it was modify it to use a linear power supply, Kitsune in California had a mod kit back then for that purpose. It was transformative in SQ. Serious. Having said this, I am completely unfamiliar with current generation of Singxer. This is just from my previous own experience.