Please help!!!!!
 

I just revently bought MOW from Gamestop to download online, you start it up with a gamestop app on my desktop. Now I'd like to buy and download some of the downloadable content packages, mainly the multiplayer packages, but it says you buy, and download it thru STEAM, which is fine but since i bought and run my version thru gamestop, will i be able to play with those DOC maps and stuff with my gamestop bought version or will i be wasting my money? thank you in advance with any help i recieve, thanks guys!!!