First, get a digital cable, and tell the player you are using it. Then go into the digital audio settings and turn DD and DTS ON and set them to bitstream, which in your case looks like /raw as Clint said.
NEXT, you need to take a look at the receiver and make sure that it is configured correctly to accept the digital input on the source (DVD, etc...) that you want to get DD/DTS on. This may or may not be automatically detected.