Cheap HDR to SDR hardware conversion?

[little-endian]

Converting 2160p to 1080p or 1080i is simple and effective enough with those cheap converters found on amazon.

While this is not your crucial concern and so neither I am sure if your approach intends to achieve decent quality or just "some" output at the end, besides the HDR to SDR tone mapping issue, I wanna make a note about the downscaling just in case:

I'd be surprised if those cheap devices do it properly in terms of not indirectly introducing at least aliasing due to just omitting samples. Don't you have any artefacts with those devices? If not, then they are post filtering properly against all odds or the UHD sources don't contain much higher frequencies (detail) than the HD counterpart to begin with.