Hey Poets,
I apologize, as it seems I misunderstood the intent of your question, originally.
I was actually kind of confused at first, because the quality of your mix didn't seem like it would have came from someone who didn't know some of this rudimentary stuff.
You do good work, obviously.
Having been in similar situations that you're currently in ... first off, I would say the most important thing to do is to keep your composure. From the tone of your post, it seems like there's a degree of urgency to this, and you really want to be able to give them what they want and still have a good mix. And that's good.
But keep in mind that most musicians are basically turds.
Or at least the ones that work with me. I'm a musician, and I'll freely admit I was once a turd. Now that we have that out of the way, remember that you were hired to mix, I'm assuming, and not master. So what would be so wrong with explaining to them that you may have reached the limits of your capabilities? That you consider yourself a very competent mixer ... but merely an adequate mastering engineer at best. And their music is SSOOOO GOOOD, that you just don't feel that you can do justice to the greatness that is their music in that regard.
That way, you can just pass the baton to someone else and say : "Here, you deal with it."
Now if this wasn't an option for me, the next thing
I personally would do would be to pull out the multiband compressor. If the beat is distorting, it isn't very likely that it's distorting accross the frequency spectrum. More than likely, it's a particular frequency band that is the culprit, and I would further guess it is the very low / sub frequencies just to make a wild guess.
If you can work a little magic with the multiband, in theory you would be able to bring up the overall volume on the whole beat while still keeping the offending frequency range in check so it doesn't distort. This is probably what a good ME would do anyway.
Lastly, when someone tells me they want something louder in the mix, and it's already unbelievably loud, the first thing I'll generally do is EQ it differently; specifically, I'll zero in on some midrange frequencies that the human ear is very sensitive to. This will raise the "perceived loudness," sometimes by a drastic amount, without actually having to raise the actual loudness at all. This is good, economical use of headroom. Making something sound louder without chewing up any additional headroom is money, in the mixing world. Any time you can do that, you're going to make it that much easier for the Mastering guy to get a louder mix.
Any time you've got any element of a mix that is very loud, but sounds like it could still come up ... it means that you're wasting valuable headroom on something that's not making the mix sound louder. It's just eating up headroom.
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) but......................
