I had made this pack for personal use, but decided to release it, so here you go.
If you have been in the nether before the Nether Update, you'll remember four music pieces that (as far as I can tell) don't play any more: Concrete Halls, Dead Voxel, Warmth, and Ballad of the Cats. Concrete Halls is my (and probably many others') favorite.
The Nether Update added a bunch of new biome-specific music for the nether, but in my opinion it sounds more like background ambience than music. This pack replaces Rubedo, the nether waste music, with Concrete Halls, both for the nostalgia and because it sounds better.
Will only work for 1.16+, simply because Rubedo isn't in any earlier versions. I guess you could use it, but nothing would happen.