Yeah, I mastered PSYCHIC EXISTENTIALISM by scissor shock, doing many of the same techniques Al described. You've heard the album -- you think it sounds decent, right? I was actually really proud of it, because I think there was a very wide-open-spaced mix, you could hear all the little nuances; I mean, there were a hundred little microsounds going on a second, and I'm still hearing sounds I don't even remember recording. The most difficult part was mixing it all together without it sounding too jumbled, something I definitely had a problem with in past recordings. I tend to try to make the drums the loudest instrument, since it's the most important instrument (to me.. and most bands). Getting a good bass sound is very important to me, too, and I made sure and panned the guitars hard right and hard left; bass was center.. other instruments like xylophone were, maybe, left 50%... marimba, right 50%.. vocals were usually dead center, or slightly to the left.. keyboards slightly to the right.. miscellanous electronics and horns, I usually just mixed all over the place (maybe a horn would start hard left and play a solo and, by the end, be hard right).
I mainly used EQ in the mastering to get rid of rumble; I removed silences, which can be tricky when workingw with microsounds as I do since it removes elements of the mix. Or, it can. I gently tweaked the 30 band equalizer to get just the right sound I need -- usually a bit dark, but not murky.
Honestly, it was a very difficult album to master since the songs are so fast and so full of sound, but I am very proud of the job I did, I got it sounding just as I wanted, and the reception has been surprisingly good. I am a perfectionist, though, and I've been producing, mixing, and mastering my albums, and others albums, for 13 years now. It's just something you really have to keep messing around with. But experimenting is really fun.