RetroArch runs flawlessly on my Xperia Z3c (Snapdragon 801, Adreno 330). I can also use filters e.g. in Gambatte the classic GB style with dot matrix without any problems. On the Mi TV Box (Cortex A53, Mali 450) Gambatte runs only with very basic filtering. When I select a more complex filter the menu will start to slow down and the game becomes unplayable. As far as my research went, the two systems should be very similar performance wise. Am I missing something? Any suggestions for configuration? I did already try nightly builds without improvements. Thanks for any help!
Are you using video filters or shaders? If filters, try some shaders instead. That will move the calculations from the CPU to the GPU. If shaders, you can try some others to see if others perform any better.
My bad, I meant shaders not filters. The one I’m using in gambatte is handheld/gameboy
So, the Adreno 330 seems to support OpenGL ES 3.0 while the Mali 450 only supports ES 2.0. Could that be the reason for the difference in performance? Just trying to shed some light on this mystery 
I suppose your tvbox is an amlogic s800 or s900 series. They are great for video playback, not so great for gaming, For gaming a tvbox with RK3288 is your choice (if you want something cheap). Certainly your tvbox is much weaker in both cpu and GPU than the snapdragon 801 you mention.