So I spent some time poking around the mix. It's not done yet, but I have a better idea of what's going on.
The problem is that Sally's very nice drum line is eating a lot of the sonic space in the mix. This wouldn't be hard to work around, except that I have a lot of voices that show up on the chorus and they push the mix over the edge. As a result, everything ends up sounding frighteningly compressed and squashed.
I played around with the compression, starting at a lower threshold, which -- given the presence of makeup gain -- pushes up the parts of the mix that are at a lower volume. This helps quite a bit. I think what I want to do is duck the drums just a bit on the choruses to make more space for the vocals, which should cause them to pop forward in the mix. I may push the lead vocal up a bit on the choruses too and see how that all balances.
But that's tomorrow's problem (since I spent the rest of the evening watching TV, Monday night having about two and a half hours of stuff I want to see).