With popular apps such as Youtube I see DPI settings all the way from "no dpi" up to 480 dpi at a site like apkmirror.
For the instruction set I'm 99 percent sure ARM or ARM64 is proper, but I'm not sure which one is best.
I don't think the Mi Box uses an x86 architecture.
I think "no dpi" works on all DPIs so try that one.
I would check out this article for more info. There's a link in there for this article on CPU instruction sets.