Panasonic DMP BDT-500 : How do I get Bitstream through to my Onkyo tx-sr705 receiver?

Hi all, I've had my new 500 about a week now and while there is a definite step up in sound and picture quality from my old PS3 I still can't get it to output in Bitstream to my amp. I've got an HDMI going direct to my Pioneer 5090 TV via the HDMI Main out and the 2nd HDMI SUB out to my Onkyo Tx-sr705. I've selected Bitstream digital audio on the 500's set up options page but on the 705's display it shows: PCM fs=48kHz and defaults the DSP mode to the prefered DSP mode for PCM eg stereo, THX etc... Any advice you may have will be greatly received as it is really starting to annoy me now!!!