Boo,
Are you using that Rogue Roller PA? That's a mono amp, and it won't matter how many channels you use - it'll always be mono. If the one voice is louder than the other - adjust the level on the input channel of the mixer. And BTW - the Korg doesn't have a "gender" choice - just pitch.
You are probably loosing bass response because of an "out of phase" situation caused by the mono amp. In effect, you have the same signal being sent to 2 channels. Go back to the old way if it sounds better.