I've never tried this, but I can't imagine it working properly. With what you're suggesting, if the camera is well behind the player, but the listener is on the camera, and a sound plays just behind the player, it'll sound like it's coming from behind (on a surround sound system), even though it's happening in front of the player. For regular sound systems, you could perform the same thought experiment with the sound coming to the right of the player, but still in front of the camera, the sound would come from the right speaker instead of both. For this reason I really don't think changing the forward/up vectors would do anything.