Hmm, well I have recently been trying one of the approaches in Gieseking & Leimer's book on piano technique (try search for pdf): this is to play a Bach 2-part invention, first HS the HT, at extremely slow speed, e.g. quaver (1/8) = 60 bpm (a discreet background metronome tick is advisable). The core idea is to listen, with MAXIMUM ATTENTION, to every single note produced and thus gain a proper sound production mechanism, perfectly calibrated to the musical demands from pppp to ffff. It may sound trivial, but believe me, try if for a week and I think you will see results.