I've been trying to get my Onkyo receiver to output Dolby Digital Surround sound, but for some reason it will only output in PCM. I've tried three different DVD's all with the Dolby Digital symbol stamped on them. I've gone into each menu on each DVD and selected Dolby Digital EX 5.1 Surround sound. The only thing I can think of is maybe I'm not up to date on all the new formats and the EX is something my receiver doesn't support. It's running through an optical cable. I just can't figure out what I'm doing wrong. Anyone with this system have a similar problem or am I just completely off track of what I should be doing?