The original developer of Cog doesn't seem to have updated it for years. Fortunately, it is open source and there are a couple of forks. I've personally compiled my own copy, but you might have better luck with a version from http://mamburu.net/cog/ (though that one is still from 2013). In any case, I loathe SHN with a passion, so I always convert them to FLAC anyway. No, I never use iTunes as a media player, so the fact that it can't play FLAC (or SHN for that matter) doesn't bother me.