Absolutely completely not metal at all

Sorry about the double post but chrome's spazzing out and won't let me edit:

Listening back in the morning, the vocals really are flat and lifeless but I have no idea what I can do to them, 'cause boosting the top end even half a db brings in a shitload of sibilance

HELP MEEE
 
Hey dude! Nice mix. I'd stick to the first attempt and try this:
Even though you said it brings shitloads of sibilance, I'd try high shelfing above 6-7K about 2-3db. Just see what works best for you, small adjustments sometimes make a huge difference. You can also try a band boost at around 15k to give the vocals some air. Oh and put a de-esser after the EQ in the chain, this will cut off some annoying highs. Good luck :)