>. My question is does you run of the
> mill ADC0831 8-bit ADC have what it takes to sample a voice signal?

I'm getting 8kS/Sec on 8 channels at 10, bits interrupt driven, on an 8 MHz
AVR8535.
Along with a ton of other things going on.

As for the national part, check it's conversion time, and add in whatever
time it will take you to talk to it. IIRC they run SPI interface. Pencil out
the code to talk to it, and see if you have enough cycles left between
samples to do the rest of the job.