Eric first off what type of mics are you using? I had this problem also especially with my Senn mic... I find that different ones give different gains big time...
My EV ND767 works best when used without a mixer & kb ....but I always use a small mixer eg: Yamaha Mg06x as the pre amps with the KB & Mics it will give up more lift in volume plus more versatility in adjusting vol of mics & KB to balance it during performance ....hope this helps..