To me it almost sound like you are trying to build your own soundcard. If you haven't got a lot of experience with dsp programming and analog circuit design you are going to have a bad time. (or a really good time spending years learning it ;-)
If you are just looking for a way to get many (and extendable) audio channels into MAX or Pd or some other audio processing software, save time and money and buy something like a M-Audio Delta 1010LT it's like 170 € on e-bay (new, including shipping) You could probably get it around 100 € used. If you need more channels, just buy another one, they are linkable. see:http://www.m-audio.com/index.php?do=support.faq&ID=32f370e2c3d0712bccc9e1f292fcb135 You'd need a stationary computer though, but you can pick them up used for almost nothing these days. (at least where I live.)
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