If you want that you won't want this steam machine, HDMI 2.0 can do 4K60 HDR at 10-bit, but only with chroma subsampling (4:2:2 or 4:2:0) (not full 4:4:4).
The specs for this steam machine say HDMI 2.0, in the past I used a pulse8 HDMI CEC USB dongle with a computer which was also HDMI 2.0 iirc. I was using a 1080p projector with it but their website claims 4k support: https://www.pulse-eight.com/p/104/usb-hdmi-cec-adapter
I recently replaced a shield with an Ugoos Am6b+ running coreELEC, which works okay and supports some stuff the shield doesn't but I miss being able to run some android apps easily. I wonder if the new steam machine will support DV.