That depends on several things.
Not all TV's pass a MC HDMI audio input to an output, particularly if there's no HDMI output.
Not all TV's pass a MC output, except from whatever OTA digital channels it receives from it's own built-in ATSC tuner.
In such case, you will have no choice but to accept the two channel stereo output from the TV.
Your best bet for MC from the PS3 is to use a digital connection (Toslink/coax, whatever it takes) directly from the game to the receiver like Davemcc suggested.