In MXPlayer (I didn't try other players) hardware decode for AC3 and DTS sound tracks isn't working in this firmware. What's more from version 1.7.34 software decode for these audio codecs were removed (as it is true for almost every player from Google Play store). Only way is to install custom codecs for MXplayer and it will "magically" unmute video from internet where AC3 and DTS are most common audio codecs.
Ad 2) Known problem.
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