Wait, how does the discount with the Amex Platinum card work? (I'm within my 24 hr window for cancelling).
Amex platinum can book a free companion ticket (except taxes) when paying a refundable rate on certain premium cabin flexible tickets. It rarely works out to be better than just buying two discounted tickets but sometimes it does.
Example: If you are looking at two discounted tickets that are $2,000 each, but the refundable rate is $3500 (of which $500 is taxes), you can book through Amex and pay for one refundable ticket at $3500 and pay the $500 taxes for the second ticket, buying yourself the same two seats for the same price and getting the flexibility of refundable tickets (and also potentially other benefits like a better fare code for using miles or upgrade instruments from C to F, or even better mileage earning in some cases). I'm not sure, though, whether the companion gets full miles when booked this way or gets the same ability to upgrade, etc.