Setting the 4 fields under "Digital Audio Output" to PCM tells the player to decode any audio signal and send the decoded signal to your receiver.
Setting the 4 fields to Bitstream sends the disc's original audio codecs to the receiver and allows the receiver to decode the signal.
For 5.1 PCM tracks it does not matter. The audio for this track is not encoded in any way by any codec, so neither the player or the receiver needs to do anything. Your Onkyo will display "Multichannel" if labeled properly.
I personally prefer setting the audio settings to "Bitstream" with the Pan BD30 connected to the Onkyo 805, as to allow for the Onkyo to decode and display that it is receiving the signal for DD, TrueHD, and other encoded audio tracks.
The Secondary Audio is for a couple possible disc features: Menu audio (those clicks, snaps, etc. you get when navigating the menu and making selections), and PiP audio. If you have it set to OFF, you will NOT get any audio for menu selections, nor will you get audio for any Profile 1.1 PiP features.
However, there is a hardware issue you should be aware of: The Pan BD30 can NOT pass TrueHD audio over Bitstream if the disc has secondary audio and that option is set to ON!
As for PCM Down Conversion - leave it off.
Let me know if you need any clarification.
