Hi Joan,
I've been using the Motorola audio DSPs since the DSP56002 (early 90s). Their 24-bit architecture works very well for audio. I am now trying to use the latest DSP56721, which is a dual-core DSP563xx.
One of the main differences between members is simply the process used to fabricate them. Newer members come out that have smaller geometries, are faster, and run at lower core voltages. Typically, the lower the core voltage, the newer the part. The core of the DSP56721 runs on 1.0 volt. The older parts have a note on the website "Not recommended for new designs".
Another difference is whether or not it supports external memory. I doubt you would need external memory for your application, as there is plenty of memory internally.
None that I know of have ACD/DACs built in. They all have serial-audio interfaces (look for ESAI) that can talk to most audio codecs.
But here is why I wouldn't recommend any Freescale DSPs right now: The development software truly sucks. I have had a service request open since October, and they still haven't gotten a debugger to work. They recently dropped support for the software they recommended just 6 months ago, with nothing to replace it.
The rumors are that they will soon be discontinuing the whole DSP line. We are switching to Analog Devices.
