For me it depends. If I’m feeling lazy I just leave WoW’s music on, but if I’m feeling inspired I usually turn off WoW music and pop some Sonic the Hedgehog OSTs on youtube to make the game feel faster 
Example: https://www.youtube.com/watch?v=u_FRDqHT5y0
Miley Cyrus Party in the USA on a loop
Yes I do…I love the music of Warcraft!
I turned off music for a while because I was having trouble multi-tasking listening to podcasts or other stuff. But I left it on when I recently after I had to do an emergency computer upgrade and I haven’t seemed to have any problems.
I can’t focus on any game if I’m listening to something that’s not part of it. But I do have WoW’s music turned down decently low. I like the ambiance better. WoW music has been mediocre at best for a while.
Palia’s music I have turned up. I love it. But it’s an actual orchestra, so it’s much better.
I never focus anyway so it’s fine
When something in WoW is brand new I tend to listen to the music as I go thru it.
But after like. I dunno a month? Around that ballpark. I have to start playing other music or my brain zones out because it got bored of the atmosphere music.
Nope, I play with no music, WoW or otherwise. I don’t really get enjoyment from music generally. If I’m playing something in the background, it’ll be lectures and comedy tours.
It’s Friday Friday gotta get down on Friday
It’s been years, I can’t make it stop playing
Help me
Nope, I play with the volume off. I will turn it up for the little mini-movies though.
Usually just listen to the last DJ on Radio Paradise.
WoW music is too bland for me. I listen to my own playlists.
You must be some kind of masochist. 
For Classic (Hardcore) I leave WoW music on, with Retail I don’t.
For a few days now it’s been nothing but https://www.youtube.com/watch?v=TniUsWaHNIA on loop.
No, I usually watch videos.
But If I listen to music it’s spotify. Either some old prog or new wave shoegaze.
There ain’t no party like an S-Club party! 
Nay to the official stuff, I shuffle Two Steps from Hell songs.
I listen to youtube and mps’s while playing.
It largely depends on my mood and what I’m doing in game. If I’m farming something then I am more likely to turn WoW’s music off and my own music on, but if I’m just doing random stuff then I tend to just leave WoW’s music playing. Some days though I’m just in the mood to jam, so I’ll bring up my own music and go about my business.