I have really hard clay too. I am able to dig and move soil with my BX2200 by ripping first with a ballasted subsoiler, then pushing the FEL through the spoils with a toothbar. I will try to find a link to pics of that subsoiler and add it to this post.
O.K., found them. The ripper tooth needs to be set at an angle as close to vertical as possible. Do this by shortening your top link as much as possible. I know this seems counterintuitive, but it actually draws the shank down. I had a short bar welded to the body of the subsoiler. On that I stack free weights and put a collar on top.