On of my friends had that "slow turn-in" complaint on his Aprilia RSV-4. He was using Diablo Superbike SC1 tyres and we went with harder SC2 version to see if it improves. Just slightly, but not enough.
That bike didn't have adjustable head-angle so we went with different triple-clamps with slightly more offset for slightly less trail. Ahhh... that did it!
also. the profile of rear-tyre actually affects turn-in as well.