if 8 bits precision is enough the lowly LPC935 has 8 A/D channels and hardware IIC. This seems a logical interface chip to me.
And it has autoscan which makes the 8 channels read at full speed with no intervention (except, of course, an ISR to read the result).
I am getting quite fond of using the LPCs as "interface chips" you can preprocess the results e.g. linearize and thus free up the "main uC". As 2 clockers they are quite fast and can do a lot while servicing the processes at the same time.

Erik

PS I have no affiliation with Philips.