Seriously what is up with all the Death Metal?
I think the problem here is that people are confusing there IMPRESSION of Dwarf Fortress with what the game actually is.
People think of all the 'fun' and the deaths, and killings, and explosions and the magma, and they think "Yeah! rock music! Head banging! Totally dude!"
But Background music in a game isn't meant for that. The original guitar instrumental currently works PERFECTLY for the game as it is, because despite what WE do to the game, at its heart its a game about simple Dwarfs, out in the wilderness, trying to lead simple lives. The very elegant guitar music perfectly complements this.
If you WERE ever to add additional music to the game, I would suggest a system where the music changes as your fortress grows. That is a more logical approach then heavy rock Music blaring when you are milling around with 10 or so dwarfs...
You could have different music from when you goto Hamlet, to town, to City and finally Metropolis.
My own music suggestions?
Well if oyu mixed: THIS
http://www.youtube.com/watch?v=biaFj0S1jcsWith THIS:
http://ocremix.org/remix/OCR00638/I think oyu would have a real winner. Both of them convey a busy growing city, without breaking frm a fantasy/medieval music feel.
As ofr a Metropolis sized theme, oyu can always do :
http://www.youtube.com/view_play_list?p=BA68851B2FAE6A27&search_query=koyaanisqatsi+the+grid