Ok, this may be a drunken opionion...But even though the vox may be somewhat out of tune (I really only noticed cuz you pointed it out), I think you could give it an extra dB.  I say this as someone who doesn't quite know the lyrics to this song yet.  And I think if you would raise it a tad, just enough so you don't have to search for what's being sung, it would do well.  As long as it's not the focal point of that particular section I don't think there would be a problem.  Maybe you tried it already and it didn't work.  It's hard to know without actually hearing it.  
BTW, sorry to bring this up again, but I think the clean vocals add so much to the atmosphere of the song the way they're done.  I had the same issue with MFP...ASC at times.