Most of what you hear on radio as double pedal is triggered sounds that are tweaked by mixing. I agree that the EMAD system is nice... I use that system myself with a small portion of foam board that lightly touches both heads. Most
attack, or slap, can be achieved by using a plastic, wood, or other hard material. A felt beater will soften the bass drum
attack. If you are looking for more click in the bass drum impact you can tape a large coin to the inside of the bass drum head, or buy an impact badge, or just get creative.
If you stuff your drum with too much stuff you end up with a quiet bass drum. You could get a nice sound from a drum with very little muffling. Look at the
Evans pillow for reference. I think that pillow is a little much for what I like but for some it is perfect.
Experiment... have fun with it.