alphajay777The SU-9 mostly removes the intermodulation distortion bump present in ESS chips, while the SU-8 does not. The rest is largely cosmetic, minus the SU-9 doing MQA, which may or may not matter to you.
alphajay777https://en.m.wikipedia.org/wiki/Master_Quality_Authenticated
The TL;DR is it's a supposedly high resolution format that's used in services like TIDAL. Some people value it for that reason, but it is questionable if it's truly hi-res and not actually a somewhat lossy format used for marketing purposes.
SDK1This is correct. MQA was developed not necessarily to add quality, but specifically to add DRM.
In essence, it is just FLAC with applied digital filters, though usually, because it is "tuned up" to the human ear perception MOA sounds better than old plain vanilla FLAC at the same resolution.
When used thru digital streaming services (like Tidal, etc.) MQA is worth it IMO since it frees you from applying your own digital filters, but if you are buying files to build your own musical library MQA is superficial and very inconvenient to have actually.