The Tanix box I linked has the H6 which should be plenty. I couldn't find many benchmarks between S905X3 and H6 but the ones I found are pretty much on par. Differences could be explained by cpu frequency, ram, speed of the disk it runs on and the OS it runs on. Personally I would lean towards H6 but thats because my NanoPi's all have Allwinner chips too and they're very reliable for me. Allwinner has pretty decent Linux support as well. For me that weights heavier than anything else, but for multimedia they should both be fine. Pretty much all codecs one would need are supported by the chipsets.
