The DSP56000 was their first generation DSP core. I would go for the DSP56300-series as it has enhanced instruction set, improved architecture, more on-chip memory and higher clock rate. The chip is very pleasant for the assembly programming. There is also a freely available simulator which can be used for testing algorithms and/or getting to know the architecture. The simulator supports single stepping, break points, register views, memory views and even memory graphing etc. The same simulator can be used with the actual hardware and Motorola EVM cards, too. Very handy tool.