I have a Synology NAS and I actually think it's the best DLNA server that's available native on a NAS. You are have been using Audio Station which isn't actually the Synology DLNA server. It's their proprietary media server and like most others, it is extremely limited with regard to cataloguing and indexing, offering little more than the standard Artist/Album/Genre type menus. However, its advantage is that you can use the Audio Station web interface and mobile app to play the music.
However, you can use its DLNA Media Server instead. This means that you will only be able to play music through a DLNA player or renderer but you have more control olver how you catalogue your collection. It allows you to construct custom menus from a slightly larger rnage of tags. Not much, but it's better than usual! You have Artist, Album, Genre, Album Artist and Composer. however, Video and Picture indexing is largely non-existent and you can only browse by folder or date.
It depends exactly how you've tagged your collectionas to whether this would be useful or not.
Apart from that, the third-party Plex is also now available for installation on a Synology NAS but, again, it's not as flexible as J River for cataloguing.