Are you using the PE mode on the P75? I had that combo for a couple of years and it never sounded thin to me. I found the P75 to be lacking something with other carts, but in PE mode with the 20XL it was wonderful.
Now, if you are in PE mode I would suggest what Elizabeth recommended and try to go lower on you settings on the P75.
Now, if you are in PE mode I would suggest what Elizabeth recommended and try to go lower on you settings on the P75.