I also wanted to include this great e-mail from Twigg where he responds to a bunch of questions and comments that I had. My questions/comments are inlined (by him) with his responses. The technical depth that this guy has never fails to blow me away:

1) "I'm using a multi-band compressor for all my keys "
Typically you use a Multi Band compressor on the Master out. You can use it on individual components but you're better off just using a normal compressor as a multi band compressor expects a full frequency sound and an Keyboard or Drum hit will only be strong in a narrow band of frequencies hence a single compressor will suffice.

A good Multi Band is Ozone Isotope but any will do. I don't have a good enough ear yet for the quality difference on Multiband compressors.

2) "I've also put a compressor on my kick drum"
I haven't had much luck compressing kicks. I know people do it though. I've had more luck with just using envelopes which ultimately results in the same effect as compression except more rigid in behaviour. I try and figure out how long I want the bass decay to rumble for. If its too long, it makes the track just rumble with no room for baseline and if its too short, the kick bass frequencies don't have time to build up (kicks have treble attacks morphin to bass decays). Often I find I like it long when the track is just kick but when the baseline comes in I like it short. But just pick a length and stick with it for whole track.

No reverb and no stereo on baselines or kicks.

3) "Should I put the whole track into a compressor and then turn up the level on the drums"
Yes put it through a multi band but no you don't need to turn up the drums.

First, without the compressor, mix the track to taste. Then use the multi band compressor in ozone. I normally just loop the busy part of the song.

Settings:
Attack: I've come to realize this is the most important setting of the compressor. I like to keep this relatively wide open (about 80ms)
Here's how I think about it.

A house track is 120bpm and therefore there's 1 beat every 500ms. You're kick and kick/snare fire off and will more than likely be the items that are driving the compressor. So whenever they fire off you let 80ms pass through unchanged and then it clamps down. This gives the result of making youre track sounds more beatmatched believe it or not. All those other sounds that are a little bit early and little late that don't fall within that 80ms will be compressed. This compression strengths the feeling of rhythm in your track.

If you start to lower the attack, very quickly you start to loose the attack of your drums which is why I think you describe it as 'loose the high freqs'. The attack of a drum or any sounds for that matter gives it the rhythm and timing, and the decay gives it the tone. So lowering the attack of the compressor can weaken the timing of the sound.

80ms is a good setting for all Frequency bands. Maybe smaller (40ms) attack for the highest band.

WARNING : Too small an attack on your baseline will cause popping because the wavelength of a bass note can be on the order of 80ms. Solo the bass channel and hear if it pops.

Release and Threshold: about 100 ms release. You can experiment with this. Too small a value and you get distortion and too large and it starts to compress the track permanently.

Threshold: until your ducking the signal by about 6db or more.

A good setting for release and threshold is such that for part of the beat there's compression, and for part of it there isn't any compression.

Ratio: 3:1 to 5:1

Output Gain: Now that you've compressed the bands, you've screwed up the mix so you have to compensate with the output gain of each bands compression. Just remix it put turing up and down the outputs.

4) "What I want is a uniform wave, i.e. I don't want the section with just the drums to be a lower level; I want to use all of the available headroom (not sure if that's the right word)."

For "Uniform waveform and use all the available headroom" you use a limiter.
Here's a common misunderstanding. Limiters are a utility, not an effect. Limiters are compressors with extreme settings. Zero attack and ~0.5ms release. This can kill your music. The reason you should use them is to use your headroom efficiently. I told you about how leaving the attack wide open lets through some of the punchiness of the attacks. Well sometimes the chaos of the track will collide to produce a super attack (ie the snare hits at the exact time the baseline with the cymbal with the hats...). This will create an abnormal spike in the sound that will thereby reduce your headroom.

SO: Use the limiter in Isotope with extremely delicate settings. IE 1db of ducking at the loudest part of your song. This will make your track look like an even pipe cleaner without fucking of the sound.

"I don't want the section with just the drums to be a lower level" - If you've setup the multi band properly, then you should find that during the busy part of the song the multi band compressor is working and during the breakdowns its uncompressed thereby giving you even volume.

5) Side Chain compression is amazing and is the best way to make a track sound big and pumping. I run almost everything through it EXCEPT the cymbals and snare, WHY? because these almost always coincide with the kick. If the kick ducks the snare, then when you mute the kick, the snare will spike in volume (very bad and painful)

The most important thing to put through the SC (side chain) compressor is the baseline as it conflicts with the kick so SC'ing fixes this.
WARNING: ONce again, use a slow attack otherwise you'll distort the baseline.

TIP: The biggest tip I can give you though, is don't play your baseline note on the kick beat. Pick the in between notes and it'll never conflict. It has the knock on effect of making your baseline sounding more funky.

6) Layering kicks : I've got a great tip here too.
I typically only layer 2 kicks.
a) I pick a kick from the pool that I just like for its treble (not its bass). Infact once you've picked the kick, High pass it and remove < 100hz to get rid of the base.
b) I follow this up with a kick that's all sub. like a 909 kick or or one of the miami breaks kicks. I pick one with a long sub decay because like I said earlier you can remove the decay with the envelope. You can always remove sound, you can't add.

c) HERE's the trick!: Here's the biggest tip I can give you then. YOu have to tune your sub kick to the melody of your track. You have to pick one note that permeates the chords of your track. How? You take the sub kick and you pitch it up 1 octave. Suddenly its tone is clear you you. Try sliding it up a few semi tones and back again. Once you find a note that matches the melody of your track (preferably between 8 - 14 semitones above its natural pitch) then you pitch it down exactly one octave and now you've got a ~60hz sub kick that matches the baseline and the rest of your track. HUGE! Think about how wrong it is to play an out of tune bass note over and over again and then its clear that tuning your kick is crucial.

d) Layer the two and mix two taste. If you want more base, turn up the sub one.

NOTE: You can do this for any drum. Cymbals, snares and especially conga/bongos as they have strong clear tones. Often you can't hear what 'note' a drum is until you move it around. Then suddenly you can hear its 'tone' and then tune it to the music.

"I think I'm going to try sampling that and overlaying it."

I've tried it but never had any success. The recording is always so dirty from the other drum decays. You get bits of cymbals and hat reverb.