As great as it sounds using physics and big terms to explain something it all comes down to the body. If you're charging pow on a stiffer board, especially choppy pow whether it's heavy mashed potato style or even pushed around light stuff you get the whump factor. The nose hits it and bounces off it still sending vibrations upward into your body.
You need to use the knee flexation to absorb it. Think of it like riding moguls you don't go into it charging and expect the board to just hit the mogul and ping off it, you have to bend the knees and pump the bump keeping it going. Doesn't matter how stiff of a board you have with all the dampening agents in the world it's more knee motion than anything that's going to get you through choppy snow.
If you really want a board that's going to get you through it get something with either Pow Rocker or that is more powder specific with reverse camber. You're no longer fighting the loading and unloading of the camber and with the nose being elevated more it will help you to roll over the top of it.