Yes, follow msgohan's advice and hook up your PS3's composite cable's audio directly to the surround unit. That way you are sure that the TV isn't screwing with the audio in any way, as it may be before spitting out to the receiver through the headphone jack. Turn on any possible ProLogic II settings in the PS3's audio setup menu and in game settings menus. Then turn on ProLogic II Movie decoding mode on the receiver. Through the magic of encoding specific channels into phase and duplication tricks, the result will be full 5.1 audio. It is a little muddier than a bitstreamed Dolby Digital 5.1 signal, but it is still full, correct surround and the best you can do in this situation.
The first person that now walks in this thread and says that ProLogic II out of a console is "fake surround" simply proves their utter nub status.