Thank you Russel, i read MSC1210 datasheet and by your explanation i think i understand and learned a lot of new things from your posts. But, i have ready boards - one with AD7730, and with ADuC824/834 too. So, i have to write the firmware, and they (my boss) dont give me time right now to make a new design, with all consideration mentioned here in mind. The whole problem is that i didn't made neither one of the design, just made some improvents to the AD7730 board (to work in AC mode, not DC). So, at this very moment i must choose between AD7730, and ADuC824. And obviosly, i will do it with AD7730, cause i get the performance i need.
I am in front of a fact, that couldn't change at the moment. But thanks again all of you for the information and discussion here, it was helpful for me, and cleared things, not very clear for me before :)
I think we can close this subject?