have you used a multiband compressor on the track? Ley us know what you have already done to the track.

How did you mic the amps? If you didn't mic very close you won't get proximity effect which would help you situation here.
IF all else fails run the guitar tracks to a bus with a low end lift and play with the frequency while you're playing the song back until you're satisfied

How's the clarity of the source material? I've heard some severely detuned bands who...uh...didn't have clarity high on the list of aesthetic objectives. Hard to be clear with strings so loose you can make a slip knot in them.

Are you talking about the bass register of the guitars or the sound of the actual bass guitar????

I think he's talking about the bass guitar. Obvious sloution would be to boost the top end of the bass. One problem you're probably having is that DROP C is really a dumb idea on a standard guitar. The scale is made to tune to E. Once you drop that low, the intonation is impossible to set due to the physical size of the scale and the frets. So, you're actually getting a ton of low end dissonance and out of tune-ness as well. It's very hard to get the instruments to sit without tons and tones of eq that usually involves cutting everything below 200 on guitars...which somewhat destorys your purpose of tuning so low. When are metal bands going to start playing baritone guitars?

Neil

nope he's talking about guitars in general "guitars in the song are in Drop C (CGCFAD)"

and as long as you can adjust the neck and action of the guitar you're okay, it's just one step down anyway, it's not extraodinarily down tuned like alot of bands (once you start tuning down 2 full steps then you're in trouble)
But just a slight neck adjustment and some action adjustment you're fine.

It's only if they're really low, then you want a baritone guitar