AFP is deprecated, and you really should be avoiding it. It lacks many features of SMB, and the latest versions of OSX highly discourage it’s use. You will experience a very poor experience if you use AFP, including appearing/disappearing music, and very spotty connectivity. It’s so not worth the hassle, that in a future release, we are going to actively explain that using it can only make you sad.
Our SMB support on OSX is good, but it’s even better if you mount the drive yourself in OSX on /Volumes/XXX. We hope to do this internally in a future build. This will use the latest SMB protocol, which includes real-time file monitoring and many reliability updates. On Windows, we already do this.
Edit: OSX Roon does this now too.