Don't understand. Disable and enable DTS in stream option so you will see pop-up. Read it.
When you will play any MKV file with DTS stream, your PS3 will show it as 2 channel LPCM but receiver should detect DTS.
It is because PS3 doesn't support DTS so it is packed to LPCM 2.0 stream to force PS3 ignore this track and pass it automatically to receiver without any touch.