if a xvid is created from a DD EX source does the AC3 encoding still keep the EX part of the sound track ??? and if so is there a way to activate this EX flag on a DVD-r

yeah i know the EX is just a matrix of the 2 real channels, just dunno how, or if the EX flag can be activated by a DVD-r, im thinking there must be some way to do it in IFO editor but i havent got a clue where to start