You have ZERO idea.
"To make it simple, the difference between bitstream and PCM, is where the audio is getting decoded. If you choose PCM, audio gets decoded from DD5.1 or DTS 5.1 or DTS-HD or whatever, to PCM and then gets sent over the audio portion of HDMI to your receiver where it's converted from digital to analog and played over your speakers. If you choose bitstream, the audio track in DD5.1, DTS 5.1, DTS-HD or whatever, gets sent directly to your receiver over the audio portion of HDMI. There it gets decoded to PCM, converted from digital to analog and played over your speakers.
So really, the choice is simply a matter of where you want the audio decoded. In some cases your receiver may not support one or another audio format and the PS3 does. So, you would choose PCM so that the PS3 would decode the audio and send it to the receiver.
I should point out that it's quite difficult to do an objective comparison between the two, if there is ANY difference in volume between the 2 cases, as listeners invariably pick the louder one as being better sounding. Ideally, whether you chose PCM or bitstream, it should sound identical."