Well, attack is a vital part of getting those really low notes to cut through. The xiphos guitars are not designed to enhance attack, they seem to be built as more of a lead guitar than a rhythm guitar: that thick, fat tone. But, there are other steps you can take to enhance the attack of your guitar. First, get a nice thick, pointy pick. Icepix makes metal picks that are very nice. I bought the stainless steel ones, then dremeled them down to jazz size and gave them very sharp points. Quite a few underground metal guitarists use pointy, metal picks. Another thing you can do is switch to stainless steel strings. IDK what brands make 7 string stainless steel sets, but the difference is night and day. Also, thin gauge strings will help clear up your sound. Of course, thick strings help keep the tension better on the low B, but using 9's actually will help in hardcore music because they give you less boominess and give the guitar more of a "slugga" sound due to the slacker tension, and that "slugga" sound will give your guitar sound a more percussive attack, which helps the low notes cut through. Also, I really recommend ditching the Celestions. Celestions are too smooth for hardcore if you ask me. I'm quite partial to neodymium speakers (I'm partial to neodymium everything, really
); Eminence makes some affordable ones that are nice. But my whole point is that there is more to sound than EQ: every link in the chain is important.
And really, I think the Kerry King amp sounds like crap: warm and fuzzy. Then again, I don't think the Slayer guys really care that much about their sound. For face melting, extreme distortion there are only two options if you want clarity: use a solid state or digital amp, or use single coil pickups. I use an RM4 into a solid state head, and I use overwound P90's 95% of the time, and I have to gate so hard it's ridiculous, but compromises must be made when playing high gain.
