1.What exactly is HD audio ,do i get hd audio without an HDMI ,or with optical still i can get HD audio.
HD or High Definition audio is a 5.1 or a 7.1 codec that stores the audio in uncompressed format. If there is some compression, it will be lossless compression. What you will get is the full frequency of sound, greater clarity, and a larger soundstage.
2.what audio presets i can see on AVR ,like DTS ,Dolby,PII - example i am watching a movie Avtar which .mkv file .
my doubt does audio we get what it original format or we change it to dts ,Dolby according to our requirement on AVR,little confusion.
At the outset, you should get your source to bitstream audio. When you do that, the AVR will receive the original codec that it will decode.
Onkyo has a very useful feature called 'Listening Mode Preset'. With this, you can tell the receiver to go to a particular mode, depending upon what signal it is receiving. The best thing to do would be to set the listening mode to be the same as what the receiver receives - Dolby to Dolby, DTS to DTS, etc.
According to Onkyo, 'You can assign a default listening mode to each input source that will be selected automatically when you select each input source. For example, you can set the default listening mode to be used with Dolby Digital input signals. You can select other listening modes during playback, but the mode specified here will be resumed once the AV receiver has been set to standby.'
See page 55 of the manual.
I have fooled around with the settings, but have always found that the original codecs are the best. Many times when I changed Dolby to DTS, the system added unnecessary gain and noise. The better option would be to change the audio codecs in the media if it is available.
I have set on my playon mini pass through for audio ,as per my knowledge it should show on AVR what ever the format is movie is in from Playon right.
That plus bitstreaming and listening modes would, as the yanks say, get you to a 'you are all set' state.
Cheers