I have been flying DP Extra for almost 2 years. It is my best gasser, better than H9 33% extra. The snaps are great, heres my procedure:

1. Throttle back to 1/5 -- 1/2 if vertical -- 1 second before start
2. Small input on elevator
3. Lots of aileron and rudder, keeping some elevator
4. Neutralize elevator, reduce aileron and feed some power
5. Full power, no aileron, counter rudder (to end the snap) and elevator to trim the plane.

Just my 2c.