Same here. I'm a huge fan of heavy metal, and I loved Fanatic's music (especially for the CTF edition), but even that got old after a few months. The music for Red Eclipse is alright, but it's way too mellow for a fast-paced twitch shooter where ninja cyborgs fight to the death.
Your best solution is probably Pandora Radio. (or Last.fm if your country doesn't have access). From what you described (intense metal soundtrack with a touch of futuristic), I'd recommend making a station with Jeff Loomis, Animals as Leaders, and Two Steps from Hell, but you can add whatever kinds of music you like.
One great thing about Red Eclipse is that if you hear a song you don't like, you can use
bind P [if (= $fullscreen 1) [fullscreen 0; mousabsolute 1] [fullscreen 1]
(write it down and type it ingame using "/", or add it to your "config.cfg" file)
and use the P key to switch from fullscreen to windowed mode. When you want to do something else like change a song, just wait until you get fragged (or go into spectator mode), type P, and minimize the window. Then, when you're done, unminimize the window and press P again to go back to fullscreen.
BTW, I think that was one of the most polite posts I've ever seen on any forum on the Internet.