Parameter setting as far as I remember that is probably stored in the system config file on your memory card.
As I said though, the option is greyed out if you have it set to use the optical output (at least it is in mine, and I don't remember if the PS2 outputs sound out of the optical and regular RCA jacks simultaneously, so not having the option available if optical is enabled could be a pain if you want to use RCA out at some time in the future), but there shouldn't be any difference in the sound-level output using the optical out anyway.