I'm not real sure what you mean but I'm going to guess and say you mean vocals sound like crap through the VP150 and are breaking up or something close to it.

If I had to guess at this I would say it sounds like the VP150 has been over eq'd on the treble side. If you can, turn off all eq functions to the center and try it and post back. I would also make sure just to be on the safe side that your crossover is set at 80 or higher.