It shouldn't be limited to the same value, just different promotions.
Believe me, the gaming coupons ARE limited to the same value in any given transaction. For instance, you can't redeem TWO $15 gaming coupons together in the same transaction, but if you happen to have a $10 coupon AND a $15 one, you can stack those two together and get yourself a $25 discount on that purchase.
As for the ponits coupons (like the earn 5,000 pts. or 10,000 pts. to your SYWR account by making a purchase of a certain amount), a K-mart supervisor explained to me that those do not stack with ANY other coupons. So if you're going to use those types of coupons, then it'll have to be just the one per transaction.