Is your vibration road speed related or engine rev related? When the car starts to shake, if you knock it into neutral, do you still feel it shaking?
Here is my story from 12 months ago about how I finally resolved my car's shaking. Mine's a 640 diesel but maybe there are a few more ideas in here for you to check out.
https://www.6post.com/forums/showthread.php?t=1471811