Work with Amex since they are the ticket issuer.
Since the cancellation is outside of Delta's control I would not expect them to protect you on another carrier other than KLM or DL. Have you looked at DEN-MSP/ATL/DTW/JFK-LHR-HAM? The US-LHR will have lie-flat seats and they may be willing to put you on LH on LHR-HAM.
The cradle seats in BE, which Delta offered are not that bad - it is like sleeping in a Lazy Boy recliener. And they have 60" of pitch (distance between seats) not 60º of recline - they are more 160º of recline.
http://www.delta.com/traveling_check...te/seating.jsp