as far as I know, the Formuler Z7+ should be able to play 4K movies. My IPTV provider has several movies with this quality but I haven't been able to play any of them smoothly. I've tried using MyTVOnline and VLC player but none work. My connection speed shouldn't be a problem. I've tested playing these movies using my laptop connected via wifi and they play fine while using the receiver connected via an ethernet cable they don't.
The files are mkv files, just in case the format changes anything.