Well, it's the same model, just that the 9000 is for the US and the UK.

I am also interested in this question. Perhaps Digitec-Galaxus could help??? They are sitting at the source!

It has something to do with Hollywood Standard (and 4.4.4 parameters).
There is something about it on the internet:
https://heimkino-klang.de/shop-2...

My DP-UB9004 runs flawlessly with self-produced UHD 4K ( and 4.4.4 ) videos.

Is the successor to the 9000... improved hardware, ThX certified etc.

That's a very good question, to which I still haven't found an answer! I assume it's a non-EU model but that's just a guess.
Apart from that it's an excellent player, I'm also looking for a simple way to unzone it for US DVDs if you have a tip I'd be interested!