Risking a necro but i got a similar project in first prototype atm:
Led Cube 8x8x8 RGB driven by TLC5941 12bit ic's
All low level control (multiplexing, SPI to the drivers and timings) are done by an spartan3 that is still abit bored
the spartan3 is feed by SPI from an raspberry with 24bit/pixel data
the spartan has an brightness table for each color to translate 8bit to 12bit with nice curve
you can feed all data to the spartan via SPI, position mappings, current setting for each LED and the brightness tables.
i thinking about to put the project up here in a thread if you are interested.
regards