How do I avoid breaking the screwhead with Impact Driver
For speed and precision, I do two things.  

I pre-drill the hole.  That is especially important on hardwood.  I often use special drill bits made for screws which include the countersink.  

I drive with a speed wrench and a bit holder.   This gives speed, control and superb tactile feedback that tells you immediately when you are having some kind of a drive problem.  Once you get the knack, it becomes basically impossible to break a screw.  

Also, I don't use drywall screws for anything but drywall.  If you want a screw like that, use deck screws and consider star or square drive.