I apologize for my slow responses, I am currently a bit occupied with work these days and didn't have time to look into this in depth.
Once I get the chance, I'll come back with more!
PS: The Subsonic node should (eventually) show ALL content, including all the subfolders. When you click on it, it will recursively try to scan through all the folders and subfolders it finds, and populate the list in the end. The results are also cached locally, to avoid this sort of scan happening again the next time you open it. However, I have noticed also that sometimes it does not quite behave ideally (no feedback during scanning, no proper refresh when it's finished - instead, you need to click somewhere else and back to trigger a refresh). It's also quite slow while doing this.
This is an area I am planning to improve, but it will probably take some time during testing/changing/testing again before we get to a better solution. All the feedback you can provide, the more detailed the better, would definitely help in that direction.
If at all possible, I would prefer if you could open issues on Github directly where these are tracked, flagged accordingly (e.g. bug, enhancement, etc) and resolved. If you can't, that's fine as I am also monitoring this thread of course. ;-)