MX player has been pretty good with most formats, but if you are running DTS audio, that might be an issue. There is a new beta VLC media player that you could try out which I think handles DTS software decoding if that is the case. You could also try V Player. But in the end if I had to guess, you will need to convert your files to an acceptable format for the N7 to play it back via hardware natively - especially if you are maxing it out with software decoding.