Very informative report, David. Great pictures.
I have been to Xe katam falls just yesterday. The way down does not exists anymore, however there are still signs indicating the trail. I did it on foot only hundred meters. After that no way further. From the view point it is possible to distinguish some roofs of chinese buildings of another new hydroelectrical project very close to the falls. The road to this complex is not accessible. But...
Riding towards Sekong, just few kms after the falls there is a bridge. Soon after the bridge there is a tough trail ridable only 600-700 metres. Further only walkway. Locals told me this is a way to the bottom of the falls. Distance is about 3 to 4 kms. I was not sure to venture so faraway on walk living my bike in the forest. I walk only one km and decided to turn back. I suppose it is possible to reach only chinese buildings and not the falls.