Which 4K DVR do I want?

I've been searching online for nearly an hour and can't find the answer to this question about equipment.

To get a 4K DVR, all I can find is that I need either an XG1v4 or Xi6 box. I cannot seem to find anything that explains the difference. What is the difference? Are those both 4K DVRs? Which one is better for 4K and HDR as well as 2K video quality?