Hi Matt,
I checked out your reference track that you're sort of going for as well as the tracks you provided. In my opinion, the difference is....if you listen close to the G&C kick drum, it isn't even remotely close to where the bass guitar lies. That bass is the lowest frequency in the mix pushing about 50 Hz with a nice, tight compressor on it so it never lashes out. The kick drum is way out of the way frequency wise and is more up in the 85 Hz range where it's tigher and out of the bass guitar territory.
See that's the thing, when you want a nice low bass to stay in your mix, you have to go with a kick drum that has a bit more beater attack that also doesn't thump in any frequencies close to where the bass is. The bass is what that song is about for me. If they had the kick drum down low, they'd need to bring the bass low end to something higher. This is where carving can really help you get what you're after.
In your mixes I heard, your bass isn't down low enough in the frequency range to hit like G&C's. You'll then need to sacrifice some kick drum thump once you get down there. A good 5 string bass with new strings and a tight compressor on the 50 Hz bottom should sort this right out. Or, a DI and a pre-amps bass signal will work. You set one for the sub low area, the other for the definition.
Granted, this is a different style of music here which is more guitar oriented, but listen to how low my bass is in this. It just grabs that low end area and never lets go. Fender P custom 5 string into a Manley on one end, and a direct box on the other. Mix them together, and you get this:
http://dl.dropbox.com/u/4909348/DestinyPreview.mp3 Of course my bass there isn't as dominant as what you're looking for, but that same low end is there that never quits or gets muddy. No octaver yet pretty similar results.
-Danny