Hey soundchaser59, here's an interesting little tidbit for you (This is gonna be lengthy, but so was your OP, so I think you may actually have the patience to read it

):
Somebody once asked Michelangelo how he was able to sculpt an angel from a slab of marble and his response was: "I saw the angel in the marble and carved until I set him free."
This eventually grew into the simplified, and more commonly heard tale of a man who was seen chiseling a rock into a beautiful horse was asked, "How do you make a sculpture of a horse?" The artist responded, "I simply chisel away everything that doesn't look like a horse."
It seems lame and hippyish to use such an 'artsy-fartsy' analogy, I will be the first to admit that. If there has ever been an anti-hippy/give-me-objective-tangible-advice-or-I'll-gouge-your-eyes-out person, it is me. The thing is, that this really is the closest to an objective way to 'EQ a mix' that there is. Sweep the full spectrum of each track, and find everything that doesn't sound like a guitar, and cut it out. (Or whatever the track may be, obviously)
Glen already linked to his article on the specifics of how to do this, but I'll link again just for emphasis - since I did, in fact, originally learn this unbelievable-in-it's-simplicity-and-fundamental-
necessity technique from one of his posts on here years ago.
http://www.independentrecording.net/irn/columns/gstep/index.php?id=69
It's also worth sharing, that when I first went to work in a 'real' studio, this is the
only EQ that the producer used on
anything....ever. If something didn't sound right when recorded, but did sound right at the source, he would have the engineers adjust the microphones and re-record it - if it still didn't sound right, he would adjust the microphones himself and re-record it. Google "Mack Damon" if you want to know more about him - he had 5 Grammy nominations, last time I checked... It wouldn't be too terrible of a stretch to say "he's kind of a big deal", I suppose - lol
