First and foremost, the mic usually has a lot to do with feedback problems. Use a super-cardiod or hyper-cardiod mic only.

Next, set up the mic EQs in the keyboard's Mic Settings section, minimize the high and mid EQ and add a bit of low. This should solve your problem.

Good Luck,

Gary
_________________________
PSR-S950, TC Helicon Harmony-M, Digitech VR, Samson Q7, Sennheiser E855, Custom Console, and lots of other silly stuff!

K+E=W (Knowledge Plus Experience = Wisdom.)