You can purchase the discounted APs at Guests Services outside any park and at DtD. As the previous poster stated, you will need your blue member card (or temp card issued by the sales office, if you are a new member.)
You can purchase vouchers through the Member website or Member Services, but you'd have to activate them at at one of the guest services window anyway. The advantage to vouchers is being able to purchase the Dining Experience Card prior to your trip, if you choose to do so.