S905X is a cost effective model based on S905, the greatest spotlight is that S905X supports VP9 decoding while S905 not.
Another one is the price. As a newer model, S905X has better performance, however, the price is same or a little lower.
Last, S905X is tailored to Android 6.0, while S905 is for Android 5.1.
The following table is the detail difference between Amlogic S905, S905X and S912:
Our three typical products for your reference.
|Amlogic S905 TV Box
|Amlogic S905X TV Box
|Amlogic S912 TV Box