Do you have any other source players? (DVD, BluRay, etc)
Chances are your tv is only sending a stereo signal to the 2803 via the optical output. If you have a cable/satellite box then connect it with an optical connection straight to the 2803. If you have a box be sure to set it's audio output in the audio setup menu to Dolby Digital.
You need to setup the 2803 if you haven't already done so. Speaker distances, volumes, sizes, crossover settings, etc.
I'm entrigued with the Polk RTiA speakers. I used to have the previous RTi's which were very bright to my ears. I beleive the new RTiA's were toned down a bit and if I were in the market for new they would be on my short list. I'm not as enthusiastic about the subwoofer. It's listed as only going down to 38hz which isn't all that deep. If it's working for you then that's great but something in the 23-25hz (Polk 505, BIC F-12, etc) range would be a significant improvement.
And good luck on becoming an audiophile. I've spent 10+ years and countless amounts of money trying to become one and I'm no closer than when I started . But it's been a fun journey.
"Everyday room": Panasonic 58" Plasma, Dish HD DVR, Pioneer Elite vsx-23, BDP-23 BR, dv58avi universal dvd player, Paradigm Studio 20 V1, CC-450, Dayton HSU-10 subwoofer.
"Movie/Music room": Toshiba 65" DLP, Dish HD receiver, Marantz 7005, CC-4003, BD-7006, Polk LSI25's-LSi7's-LSiC, 2 original Dayton 10" "Mighty-Mites" subwoofers. (subject to change without notice).
Also have MB Quart Vera VS05 +.....too much to list. Help me.