Well, it's just stylistic choices. Let me respond to your comments:
1. Headphones - I still trust my AKG 240 headphones over most monitors because I begain producing in those from 15 years ago, so I really trust them. They're about $80 at Guitar Center, and WELL worth it. You should try to use some monitors because there's nothing quite like air moving around in sound, and that's how most people hear music, but it's tricky, with room treatments and getting good monitors and all. But if you stick with headpones, try those AKGs and combine your mastering with that, your car stereo, some cheap-ass boombox, and a really nice home theatre and balance you recordings accordingly.
2. As for agressive mixing, a technique I use is distortion on the drums...really makes them meaty and angry. Some people have used Amplitube or other guitar pedals to get mean sounds out of drums. I'd keep the "agression" out of the mastering process. Use a good limiter like Elephant to get it loud and bring out the details, but keep the agression on individual tracks in the mix.
3. Midrange - again, totally stylistic. You don't need to have pads or other "mid-range-like" noises. Just pump up the 500-5000hz range of your snares, percs, and hats to get midrange out of your overall track. In this one, you don't need more than 2-3db of increase in the midrange to get that meaty sound. That plus some gentle distortion, and you get a mean-ass track.
Hope that helps. Again, these are all stylistic preferences - use or abuse at will
