That MF coupon is not store-wide, and the MX5 isn't listed. Maybe if you call. I remember the days when GC hade store-wide sales of up to half off regularly. I guess they where optimistic about growth.
MF will give you the 15% off on just about anything 'excluded' from their coupons if you call/chat/email. If they don't, call back and try again. You'll get someone that knows what they're doing eventually. Worked for me anyway, and I only had to call once.