I've got the download running now, though it'll be much later in the day before I have a chance to play it. Pesky work...
For those not playing on an Xbox, Gamble said they're aiming to have the EC available on Origin before 12pm Mountain Standard Time, and Sony is expected to have it available "later in the day."
Also, CVG says
that the EX has additional dialogue options and "tweaked gameplay sequences," without going into detail on the latter.