I have one soundstream region that encompasses my entire map, and I have another soundstream region that fits my maps lake. Both of their sound streams work, it's just that there is no "fading" effect when I walk into the lake's region, the sound simply changes completely to the region's sound stream, completely blocking off the global region's.
pi3_amb_crickets is the region encompassing the entire map and
pi3_amb_crickets-frogs is the region surrounding the lake.
pi3_ambiance.snd