NOOOOOOOOOOOOOOOOOOOOOOOO MY ENTIRE REPLY WENT AWAY!!!! I'm gonna cry now... and I have to rewrite it all...
As for symphonic bands mostly having female singers, I bring Kamelot to the stand. Since their formation, they have had three singers, all male, all operatically trained in one manner or another. Their clean vocals are amazing and if they need someone to do growls, they bring someone else in or they have one of the other guys in the band to it. The lead singer for The Agonist, incidentally, is female and she has AMAZING growls for a chick. She's able to get both sides of the spectrum, clean and growls, and it's good.
Tarja Turunen, the ex-singer for Nightwish and the biggest diva on the planet, sounds amazing in Nightwish because she has the ability to change the style of her clean vocals so you're not just hearing the same thing over and over again. The band also has the skill to make all the songs sound different in one way or another. Also, if they need other vocals (male) they just use the guys in the band who also have good voices (I Wish I Had an Angel and Romanticide, for example). I find the bands in which everyone has multiple talents, from singing to instrumentals to lyrics and songwriting, are the best ones. If two band mates can switch places and make something totally new sounding, I believe that is a quality of a good band.
I already am a fan of The Agonist, but some of their songs are just brutal for the sake of being brutal, which I dislike.
Also, as a fan of Nightwish, I already know about Marco, and I do love his voice, but if they used him more, I would be happier. Than again, he did get two whole songs to himself on Dark Passion Play, except one of the songs was just because Anette got sick. By the way, he has always been there only male singer, except for in their debut album, when they had a guy from another band come in and do vocals.
That last bit is also why I love Trivium. Their lead guitarist growls, their rhythm guitarist growls, screams, and sings, and their bassist sings. The fact that they all switch off on vocals a lot, harmonize, and still manage to not miss a beat in their playing is beyond amazing. Plus, both guitarists down pick faster than freaking James Hetfield. If that doesn't prove how good they are, not much else can.