I have my PS3 hooked up to the TV via HDMI and via digital optical to my receiver. Under sound settings I have Audio Multi-Output set to "on". Under Audio Output Settings for Optical Digital I have most of the surround sound options checked, including DTS. This setup works great for me. Audio still feeds to the TV via HDMI and I can also turn on the receiver separately when I want that full sound.
PS3 -----> HDMI -----> TV
|--------> Digital Optical -----> Receiver