The audio chip is a T.I. TSC2303. It is apparently a custom chip derived from the TSC2301 or TSC2302. The whole series of chips have 2 (i.e. stereo) line-in inputs with gain control, but it is not clear that the custom chip used in the N800 actually routes the inputs outside of the package. We don't have the pinout.

The datasheet of the TSC2301 is here