I'm pretty sure FMod and Bass don't support multiple listeners anyway. As GFK says, it's kind of pointless. A better solution, I think is to maintain a single, static listener and then fake the position of your emitters so that the relative position from the listener matches that of the noise relative to the player you want to hear it. That way, both players hear their sounds in the correct relative positions. They're not going to care where their opponents sounds come from, but they are going to expect to hear them, so their expectations for that will be met too.