I think MI supports DD , DTS through hdmi out. But no Atmos support mentioned.
Also : with AV: SPDIF Out / 3.5mm audio output x 1 port
www.mi.com
Seems to be a decent player for the price. Since its android box you can install more Apps comparing to Fire stick.
Not sure , whether there are any real users of MI box in this forum. You may check.