Ouch.
Well you want to always make sure you're using a line level output into a line level input. Amp heads tend to be dangerous things to plug into a PC. Not to mention, you probably won't get such a great sound either. BUT, even without a v-amp there are ways to compensate... such as post processing with a plugin such as Revalver. Just use enough distortion with the head to get a crunch, keep the mids up and the bass and treble moderate and you will get the body of the sound needed to get a good tone in post processing.
Alternatively if you had a v-amp you could use its speaker simulators, or just bypass the Warhead altogether. or use both, and record one rhythm with each, for more distinctive stereo seperation and a bigger "wall of sound".
Yeah I have liked Dimmu since Stormblast days, and the latest one is good too. Wouldn't call them BM so much nowadays though. Symphonic Death/Black maybe? I dunno. I only have one Old Man's Child album, but they seem pretty good too.
When I went to your site I instantly recognized "Cradle To Enslave", being one of my favorite CoF tunes.. fit the site very well too.