no, unfortunately there are no readynas devices which support 4k, which for best efficiency needs a gpu (either gpu in the cpu or external gpu card).
if you want a nas that can support 4k transcoding (which you should not be doing anyway), you will need to look at other brands. qnap/synology have various models that either accept a gpu card or have a cpu that has a gpu built in.
I can’t help you with those, though there are plenty of threads in those forum sections you should read if that is something you are interested in.
for 4k, see also this thread @ Plex, 4k, transcoding, and you - aka the rules of 4k - a FAQ which make help clarify the issues with 4k before you jump in that deep end of the pool.
