As I was enjoying using /playsound to listen to the new music while in the Overworld in Creative mode, Overworld Creative music then begun playing over the top of it (it was Aria Math, which is a piece of music I would have never thought I'd complain about)! Even when using the "music" channel with the /playsound, this still would happen, and so to listen to the new music uninterrupted I had to play the nether music in the ambient channel and repeatedly using /stopsound to smother any other music that begun to play.
I would expect that using the /playsound in the music channel would prevent other in-game music being generated over the top of it, and so I have reported this.
How to recreate:
1. Go to the Overworld and wait until no music is playing, or /stopsound all music sounds
2. Type a command similar to the following (this was the command I used when I discovered it): /playsound minecraft:music.nether.basalt_deltas music
3. Wait and eventually in-game Overworld music will probably play, unless my situation was more specific than I realise