I dont think you can do both consoles at the same time, ........ several months ago i was thinking about buying an XBox  to replace my PS3 ....... I contacted Tech support and asked more or less the same question, .... Support told me yes, BUT i would need the recipt number i got from the PlayStation store along with other information about the transaction, send that to Activision (cant remember what dept) and that it would be applied to the Xbox Account,  and it could take up to 72 hrs to take effect......... It sounded like a headache to me, and i decided to stay with the PS3     You should contact support  before trying it