Hi,
It can’t goes higher than 50 Mb/s read and write
Known limitation with 3.x kernel. You may want to try the 4.9 kernel provided by Odroid and Meveric’s repo (still in devolpment):
https://github.com/Fourdee/DietPi/issues/926#issue-226591577
I get around 80MB/s transfer rates with 4.9:
https://github.com/Fourdee/DietPi/issues/899#issuecomment-298228750
And an other thing… I prefered to use this odroid for media center too, like the raspberry pi can used, but i got little scratchy noise, and cracks in audio (they were really little, but bad enough to make anoying the homecinema); and the video was also a bit laggy, like the line goes to break sometimes.
I personally use a Odroid C2 for media centre, so cant offer any advice. Although, you may want to check on the official Odroid forums if other users are reporting the same issues with XU4.