So after opt-in we will have same amount of SYM on a different chain and we can keep same amount of XEM on old chain?
Did i get it correctly?
Yes after opt-in you get XYM on new chain in equal amount of XEM on old chan that you had on the date of the snapshot .
You do not loose XEM on old chain. You keep them because there is not coin burning or swapping involved.
Don't make the mistake of thinking you won't lose Xem. Highest probably Xem will lose value because of the 2 chains and Xym will be better (at least that's what they try to make us believe). Just look at other blockchain projects who had a similar development -> it didn't end up well. The smart people will dump a day or two before the snapshot. Only the gullible will be left holding the bag, thinking that they will have gained twice the value. Don't let the Foundation trick you by telling you that they will figure out a way to keep the Xem chain alive.