No surround sound from MKV files

WD Legacy Products WD TV Live Streaming
4

Hi

I have down graded the firmware to 1.04.12 but still no luck in getting surround sound. I have tried both HDMI pass through and optical pass through with no success. I have selected the formats my amp supports and gone to settings-restart after changing the settings, still nothing. What firmware are others using that allows DTS playback? Thanks.