Do you have any issue with emby or jellyfin?
I have to re install them and see. I used them only with my internal network and had no problems. Remotely though is a whole different situation. I ll let you know when I try. For Jellyfin there is no subdomain.confs file as you noticed if you copy and modify the airsonic one I can t see the point ot even try since you mentioned that airsonic's also is a deviation of libresonic.
Probably emby is the way to go. Can you confirm that it can be arranged in a way in order to see from left panel letters which corresponds to artists even though I have upper folders as genres and inside of them the artists. Confusing until you study the picture below
A darker theme would meake it even more appealing to the eye.