Just wondering if hdmi audio was going to sound better than an optical cable. I know that they are both digital, but I don't know if you can get dolby trueHD with an optical cable.
You will need to use an HDMI cable and equipment that works with HDMI version 1.3 or later.
Remember your disc (source material) must be encoded with a Dolby TrueHD track, and all components (disc players/receivers) must also be Dolby TrueHD certified to hear Dolby TrueHD.
These articles from Dolby's website will explain things further.