I think their water requirements and the reason they crash on import are related, but maybe not in the way some people think. I don't think they crash because they cannot acclimate to harder, more alkaline water, but because of the conditions brought about by said water.
Panda uaru and Pterophyllum altum are very similar. Their initial acclimation often proves disastrous, but once you have them through it, they are often just as tough as any other cichlid. I believe that it is not the actual higher pH or hardness that gets them, but the fact that blackwater species are coming from very pure, nearly sterile water. Then they're put into vats and aquariums under stress, where they're introduced to various bacteria and pathogens in levels higher than they've ever encountered. I believe their immune system, weakened by stress, is often overwhelmed by these pathogens which leads to the crash. They almost always crash because of something like velvet, bacterial infection, columnaris, etc.
Most people who have luck acclimating altums and panda uaru do so with very soft, acidic water and also a round of prophylactic medications. I know people who immediately bring them in and start treating them.
I do not think healthy, acclimated pandas have a problem adapting to harder, more alkaline water. I have seen them happily living in it. They will eat, and fight, and act like any other cichlid. However, most will eventually develop HITH pits regardless of how clean you keep the water, and it will progress until the fish are gone. It's a gradual process, and though the fish act unaffected, I still suspect it's because the water is too hard.