Custom Music Server & App Development

I need a music server for home and a corresponding mobile-and-desktop app with a built-in, gapless music player for lossless (16bit) FLAC. Ideally I'd need android, iOS, Mac OS and Windows (casually asking for the moon). The server would need to be able to handle a half-dozen simultaneous connections from across the world (I understand part of this will have to do with my home internet setup) and needs to allow downloads. It's the same concept as Jellyfin or Plex, those are just over-engineered for this purpose. It needs a main page (scroll) displaying a total of roughly 2000 live concert recordings, with album art and info for each. Files with all necessary metadata are on a local drive. Upon selecting the album on the first screen, you're taken to a second screen that lists the songs (with respective art again), playable individually and/or in sequence. NB the screenshots are from Plex. The basic idea is there but there are several tweaks to add