Used coil LOL.... How could the boost blow out the spark? The valve is closed when it sparks. at 6500 RPM what is the shock wave doing inside the intake? It might be you hit the limit the manifold can run. How is it modified? It could be the shock wave is travailing up one runner bouncing around and into another at the wrong time. It could be somthing as simple as changing the length of turbo pipe before the throttle body to break up the shock wave. Then there is the amount of time it takes for the valve to accelerate and the spring Frequency causing the valve to hesitate on closing by 1 or 2 thousands. This could translate to more as the cam ramp falls away from the follower and the frequency bounce is in the wrong direction.
You need to talk with an Indy car engine builder or a motorcycle engine builder and pick there brain.