bearfoil
To isolate massive vibratory impetus would more than likely involve strengthening the Shafts by adding metal. Inside Diameter? Outside? Both?
the strange thing with vibrations is that sometimes you can get better results by getting the item actually lighter (remember the famous story of Mr Citroen?). The trick is to get away from certain frequency and you can move up or down in frequency by getting the part stiffer or more flexible, lighter or heavier, or both
900 has different proportions to 800 so the internal structure frequencies has changed and solutions from 800 might not fit the new engine. A new equilibrium has to be searched for.