A new hybrid approach to digital keyboard playing is presented, where the actual acoustic sounds from a digital keyboard are captured with contact microphones and applied as excitation signals to a digital model of a prepared piano, i.e., an extended wave-guide model of strings with the possibility of stopping and muting the strings at arbitrary positions. The parameters of the string model are controlled through TouchKeys multitouch sensors on each key, combined with MIDI data and acoustic signals from the digital keyboard frame, using a novel mapping. The instrument is evaluated from a performing musician's perspective, and emerging playing techniques are discussed. Since the instrument is a hybrid acoustic-digital system with several feedback paths between the domains, it provides for expressive and dynamic playing, with qualities approaching that of an acoustic instrument, yet with new kinds of control. The contributions are two-fold. First, the use of acoustic sounds from a physical keyboard for excitations and resonances results in a novel hybrid keyboard instrument in itself. Second, the digital model of "inside piano" playing, using multitouch keyboard data, allows for performance techniques going far beyond conventional keyboard playing.