I've been thinking for a while now how it works to be Christian and a fan of metal, ie. Christian metalhead, especially death and black metal amongst many other types. Alot of this kind of music have very negative lyrics including extreme violence and satanism. Do these lyrics affect me and am I giving my money to real satanists? It is also worrisome that my choice in music often reflects how I am emotionally.
There is definitely alot of Christian metal out there so I tried out Demon Hunter and Extol, but the former sounds like metalcore which I find boring and Extol was decent but sounded like a not as good version of Opeth. Hopefully I'll find more out there that I will really like.
I don't think the lyrics of black/death metal bands affect me much because of the simple practical fact that it's hard to make out what the singer is saying anyway! But after many listenings I have found I got used to Dimmu Borgir's singer and could eventually understand what he's saying. So, I listen to them a bit less but I find their riffs and melodies so good I don't think I'll ever totally stop. I decided to draw the line at concerts, they came here not so long ago and I decided not to go. The atmosphere was probably not suitable for a Christian.
But I think my biggest reason for continuing to listen to death/black metal (other than the growling, riffs, interesting chord progressions, solos and double-bass drums) is because of human nature. It is rare and difficult for most people to ascribe to ideals (whether Christian or not) seriously, and not just when it is convenient or popular to do so. Most of these bands use dark subject matter as theatrical entertainment and to get attention and sometimes to even poke fun at themselves. Even Dimmu Borgir doesn't mind that on Metalocalypse there's a fast food chain called Dimmu Burger. Their singer even made a voice appearance in the show (I think). And I personally love the over-the-top, cheesy posturing they do. Even the wonderful death growling is powerful but also cookie-monster-like at the same time!
Also, I prefer to hear about people struggling or thinking about the concept of God rather than totally ignoring the idea and singing about 'love', lust and money.
As for the link between the music I listen to and my emotional health, I think my choice in music simply is unconsciously affected by my emotions and not the other way around. But what we choose to focus on is important, afterall Jesus has told us to turn our eyes on him. So, I've got to sing and play more praise songs, like my favorite: Be Thou My Vision. It'll be a struggle since I just don't feel like it these days but I've got to. I'll do it right now!

Dimmu Borgir strutting their silly awesome stuff