I agree, using controlled arm weight is very important. Also, it has helped me if I (very) slightly depress all of the keys of the chord before it is time to play it - this way the hammers move slightly forward - and then just let my arm drop when it is time for it to sound. This way the hammers don't have as much distance/time to accelerate. The resulting sound will be soft, but most likely all of the notes will still come out.
It takes some practice to learn, but it does work - I got the idea from watching a video of Horowitz play the very end of Schumann's Traumerei. There might be better metods... I don't know.
Btw, with this method it is probably harder to voice chords, unless you practice that all over too.