You need to have a Delta Amex card in order to use PWM. The Pay with Miles option will show on the check-out page if you have a Delta Amex card and are logged into your Delta account. You will earn full MQM's and partial MQD's (based on portion paid with cash).
Thanks, I just called Delta to confirm this. Not great, because it's 10,000 miles to save $100.
I thought this thread was about a "regular" AMEX and the ability to go through AMEX travel to book an awards ticket and earning MQMs. That would be the dream! But I currently transfer over points to Skymiles 1 for 1 when I'm ready to redeem for a flight.