HDMI cables can be had pretty inexpensively and keep your cable count low. Your Sony can internally decode TrueHD, but not DTS-HD Master Audio. It can, however, *read* DTS-HD Master Audio and send the resulting PCM bitstream over HDMI to be decoded by an AV processor such as your Onkyo.
So connect your HDMI cable from the Blu-ray player to your Onkyo and let it do all the digital decoding. Then use a second HDMI cable to send the video on to your TV. Letting the Onkyo do the HDMI switching becomes more convenient as you add an HD cable or DVR box, and perhaps other HD sources such as over-the-air HD or a Playstation 3.
These lossless surround formats require too much bandwith to be sent over a coax or toslink digital connection.
So connect your HDMI cable from the Blu-ray player to your Onkyo and let it do all the digital decoding. Then use a second HDMI cable to send the video on to your TV. Letting the Onkyo do the HDMI switching becomes more convenient as you add an HD cable or DVR box, and perhaps other HD sources such as over-the-air HD or a Playstation 3.
These lossless surround formats require too much bandwith to be sent over a coax or toslink digital connection.