The Metasaxophone is an acoustic tenor saxophone retrofitted with an onboard computer microprocessor and an array of sensors that convert performance data into MIDI control messages. The instrument has additionally been outfitted with a unique microphone system that allows for detailed control of the amplified sound. While maintaining full acoustic functionality it is also a versatile MIDI controller and an electric instrument. A primary motivation behind the Metasaxophone is to put signal processing under direct expressive control of the performer. Through the combination of gestural and audio performance control, employing both discrete and continuous multilayered mapping strategies, the Metasaxophone can be adapted for a wide range of musical purposes. This paper explores the artistic and technical development of the instrument, as well as new conceptions of musical mappings arising from the enhanced interface.