AC-3 on NitoTV doesn't work

Hi.
I’ve problem with AC-3 sound on NitoTV. When I try opening movie files with ac-3 sound via Mplayer there is rattling sound.
I’ve AC-3 passthrough enabled in maitenance and in Mplayer settings and Mplayer as default player.
All my plugins are up to date.
If I try to open without AC-3 enabled, sound is ok (stereo).
When I try to open same files in Quick Time there is only stereo sound. There is no problem with AC-3 sound in full dvd files.
But when I open this movie in Sapphire there is full 5.1 AC-3 sound without this issue (Quick Time as a player). Unfortunately this is not for me because problem with subtitles in my language. I need Mplayer to play movies.
Any help ?