I just booked a flight from PVD-TXL via AMS on KL for $582 (for a pleasant MR)-- the routing:

23 May
16:13 Providence, RI (PVD)
18:28 Detroit, MI (DTW)
KL 5584

23 May
19:10 Detroit, MI (DTW)
9:00 Amsterdam, Netherlands (AMS)
KL 6036

24 May
10:15 Amsterdam, Netherlands (AMS)
11:30 Berlin (Tegel), Germany (TXL)
KL 1823

25 May
10:30 Berlin (Tegel), Germany (TXL)
11:55 Amsterdam, Netherlands (AMS)
KL 1822

25 May
13:05 Amsterdam, Netherlands (AMS)
15:40 Detroit, MI (DTW)
KL 6035

25 May
17:28 Detroit, MI (DTW)
19:20 Providence, RI (PVD)
KL 5200

However, I did not book on delta.com as the fare that the system kicked out was $2,290.54 (M class, even when I selected "lowest fares"). Is there something that I am missing?