Hmm... Well, if I understand your question correctly, it seems like you are looking to EQ the vocals. You can use a spectrum analyzer to figure out where the peaks of the audio are at, (for instance, if the vocal has really loud frequencies at 4000 Hz, you would use EQ, and decrease the volume of the frequencies at 4000 Hz (or whatever the frequencies are). There may be more than one frequency making the vocal sound harsh too, so you may have to decrease the volume at several different frequencies.
In my experience, when the vocal has been really harsh, EQ has helped out many a time. (Although I'm still a little unsure of what the question is exactly.)
I'm unsure if your DAW has an eq or a spectrum analyzer, but if not, you could try a third party EQ and spectrum analyzer. Izotope is a really good plugin for eq and mastering. I'm not sure if it's free, though.