Ya, yep I misunderstood this too... it's easy to do as I usually think of the generic "pic" as some embedded processor not necessarily a simple microcontroller.
Well, the other thing I had thought of, and this is a completely different idea along the lines of DSP - coming at this from the software engineer side of my brain, is to use one of those really small really cheap PIII/PIV "cube" PCs (
http://www.nextgenelectronics.com/gmaxca2.php, or there are a lot of old PII systems out there too) that you can pick up for a couple of $100. Then, it might be easier/cheaper to:
1) build an interface to an on-board sound card on one of these small PCs -> then presto you have the A/D D/A interface - I'm thinking this is like a lm386 interface to give the sound card interface the right match - kind of like the headphone amp...
2) use a cheap midi interface for commands
3) using a quasi-real-time Linux kernel, at the end of the Linux init process, program in a sample/process loop that ran continuously in user space that is controlled via midi. This program could then have all kinds of libraries for all kinds of different algorithms used to process sound.
You would have to use this as an "appliance" - that is you don't rely on a keyboard or video unless you plug them in - so the only things you have plugged into it are a midi cable - running to a midi controller - and a power cable.
The main problems to using a PC for effects I think has been: The delay that is caused by the OS's scheduler, but I think there are ways to mitigate that with a real-time kernel; the fragility of the normal PC - which I think is much better with those small cube PCs; and, the cable-age that makes them a pain to take anywhere - which I think you really only need a midi and a power cable in the end.
This way you would have all of the normal PC-like interfaces when you wanted them, add as much memory as you want, work in C/C++, asm... choose your language

, and it would be completely portable (that is you could migrate all of your code to another box set up the same way...).
This approach reduces the complexity down to a software problem that everyone could contribute to - sharing algorithms for reverbs/delays....
Just a thought, but I bet it would work - thoughts?