I haven't used soundscapes just yet, but when using ambient_generics, I've noticed some sounds won't actually work. I'm still very new with the source tools so I haven't gotten too involved with sound or map file management just yet. I assume this is because, by default, there is a limited selection of sounds you're allowed to use in TF2... or something. i'm not sure if the same can be said with soundscapes.
wish i could help more, it's just something i noticed when placing sounds in my environment.
i noticed the
ABS resource pack has a soundscape library. i'm not sure if that is something you'd be interested in leveraging. i planned on hitting that up once i seriously delve into that territory. it also points to a tutorial that might help. again, i have no idea, just trying to help, so, take what i say with a grain of salt.