To be honest 'guitar pedal' and 'quality' don't go together, so it's not really an issue.
I would suggest you first worry about the processing, and there are a number of DSP chips you could use to evaluate that side of things, which will include suitable ADC's and DAC's which should be plenty good enough for this purpose.
If you then find you want more quality?, then you can expand from there - bearing in mind the higher the sampling resolution the more processing power and memory the DSP will need.