I still use X windows under linux (rather than wayland), and unlike Windows there is a clear separation between the machine with the screen (the X server), and the machine requesting graphical services (the X client)
When I execute gqrx on the XU3, with the LimeSDR plugged into its USB3, it works ok if I use another Linux machine (MMM) as the X server (that is, on the XU3 I type
Performance will be limited by the XU3 only having 100 MBits/s ethernet - over which all the graphical output must flow. On the XU4 there is a 1G ethernet driven from USB3 not USB2, so shouldn't be a bottleneck
If I attempt to use the local screen (connected via HDMI), then sometimes the screen goes black for several seconds - I suspect a GPU stall and reload. Unfortunately whatever gqrx does triggers this immediately, and the display never recovers until X is restarted.
http://forum.odroid.com/viewtopic.php?f=99&t=16362 or google 'Mali black screen bug' to confirm it's well known, and not fixed in many months. Whose job to fix?
The machine is by hardkernel in south korea, who supply the customised kernel and X server
The processor by Samsung
The GPU silicon design may be from ARM https://developer.arm.com/products/software/mali-drivers/user-space
The chance of you or I having any influence on companies of this size is probably almost zero. So I recommend avoiding the XU3 and XU4, unless you can find someone else who has succeeded in running whatever you want to run, AND who is prepared to tell you the exact versions of the software that work for them. (Real pity- a great little machine - but I wanted to use the local display, and it simply is too unstable)