Agh not this again! Noooo! :b
You NEVER NEVER EVER do ANYTHING with your "gut". Pushing with your stomach (or gut) will make you end up like Chris Barnes (wrote-off voice in a wrote-off band)... ppl say that you shouldn't sing with your throat or vice-versa, but the truth is neither.
You have to learn to control your diaphragm to limit the air escaping through your lips (I find a lot of ppl call that "singing with your gut", but that's a pretty horrible desc)... and shape the sound with your lips and throat. It makes absolutely no sense at all to say "sing with your gut" or "throat". Unfortunately it really can never be fully explained in words how to sing. It's just something you have to learn how to do with lots of practice (and probably at least ten times as much resting as singing for growls). Personally, I find if you almost growl like a dog, but do the human version of it, then you will discover your growl voice. It's a REALLY good idea to learn how to sing normally before you try growls! If you can't sing for a few hours on end, don't expect to be able to growl for a loooooong time, sorry. I've found excellent sites with search engines before who can explain it much better than I, so I won't bother. Just don't push, let it all flow. If it ever hurts or feels really strange, you're almost definitely doing it wrong.
Now, that was to just growl, basically (and I again recommend you search on the net for multiple sites to learn from)... to growl like ALEXI is another story. Alexi is a picture-perfect growler. He really understands the techniques of singing -and- growling, and uses them. He sings, but then modifies it with a growl (on the studio albums that is... when he's playing live he usually ends up just yelling and screaming cause he gets so excited, hahaha... same with Kim). This is the most difficult BUT safe way to growl, and it also sounds the best (imo). If Alexi doesn't ruin his voice screaming live, he will be able to sing for many more years. It's too bad that everyone I've ever heard try to imitate him has done it completely and absolutely wrong...
So if you want to learn how to sing like Alexi, sing without growls for at least 2 or so years (maybe as many as five), and then growl for several more years to come. And you probably still won't sound at all like him. But hey, that's why there's so many different-sounding singers... well I shouldn't say it's that hard to sing like him, but it is that hard to sing like him for any longer than 5-10 minutes.

Hope I helped a little, and made you think about how much of a huge commitment it is to sound great and not ruin your voice for life. Singing is just as complex as any other instrument (I'd say it's by far the most complex because your instrument is a part of your body and everyday life). Good luck anyhow.