gmajs, is appears from what you posted that your trailer came with ST235/80R16C rated tires, which I am not sure exist. There are ST235/80R16 D(8ply rating) and E(10ply rating) rated tires commonly installed.
Also the Michelin XPS Ribs are LT235/85R16E tires rated to 3042 pounds each not ST tires.
So 6x3042 gives you a 18252 capacity on the three axles, which is great, and you most likely will be able to run them trouble free for 7 or 8 years, if they were fresh when you bought them. So excellent choice.
Chris