Hey Thyname,
Congrats on your new purchase.
I looked up TX-SR804 on the web and it seems that the receiver does not have decoders for Dolby True HD or DTC HD Master. Which means you will have to use the audio decoders your BD player has. Personally, I prefer setting the player to bitstream the audio signal and let me receiver do the decoding.
In your BD player menu, you should have the option to turn these decoders on (in audio settings or somewhere. The options maybe 'bitstream' or 'PCM', you will have to choose PCM). You should be able to experience HD sound with your setup, its just that your receiver will not show Dolby HD or DTS HD Master on its display, instead it will say PCM.
Hope this helps.
