You have a good point, the juxtaposition of the intense battle scenes with the mellow music was an interesting contast, even if I don't care for that particular style. I was really being kind of tongue-in-cheek about them playing metal, anyway.I'm not even a diehard metal fan or anything... though I must say, it's really good workout music!
Yeah...just think of it as them giving you a break in the heavy and often grim action of the war. That's what I look at it as...
They were just trying to put a little light fun into DS9 here and there was all. And when they where trying to achieve that, they often reached back into classic film and the personalities that came out of classic film. So you had Vic Fontaine doing the 'Sinatra Wise-Guy Musical' thing...and you had Bashir as a James Bond-ish type guy...and you had the Ferengi reaching back into 1950's scifi (Little Green Men) and The Magnificent Seven (The Magnificent Ferengi).
Truthfully, I think that the DS9 writers, when they needed to get away from writing heavy war episode after war episode and coordinating with each other on all manner of minutia regarding the Dominion War storyline, fell back quite frequently on classic film. I think they sat there and said, "Okay...you know guys...I really love Bond. And Bashir is, like tailor made for doing something with that. Let's do an over-the-top funny spin on Bond!" Or one of them probably really loved Sinatra and wanted to to a rat-packish storyline...and so Vic Fontaine...and eventually Badda Bing...was born. And NOTHING is more ridiculous than The Magnificent Ferengi...and especially so when viewed in the context of the movie that spawned it - The Magnificent Seven.
The DS9 writers actually spoofed a fair amount of classic film. Vic/Sinatra's Ratpack was only the tip of the iceberg.

And as a complete aside, I agree with you (although in my own way) about workout music. My running playlists have always been chock full of Pearl Jam, Springsteen, Queen, and some other bands that have reputations for 'high energy'.
Can't say as Sinatra is on any of my running play lists...although a couple of his albums are on my iPod.
