I bought an iMac in the US 2 years ago for my family in the Philippines. I checked it in with CO on the EWR-ZRH non-stop service, no questions asked, they just put fragile stickers all over the box. The box arrived in ZRH undamaged. The trip to the Philippines was even crazier: DL ZRH-ATL-LAX (stop), CO LAX-HNL-GUM-MNL. The iMac made it unharmed to MNL! I always made sure it was secured in the original package (lots of styrofoam) and hat fragile stickers and my address all around the box. So from my point of view, it's doable… but I didn't fly KLM…

BTW, I made a trip report about this: see here. You can spot the box in the first picture.