Audi A8 stalls when you take off

The first thing to do would be to have the trouble codes checked. Any Advance Auto or Auto Zone will do this for free.
Then, if nothing comes up, check the fuel pressure. Both aforementioned stores have a test tool on a loaner basis with adapters for the test port on the fuel rail.

Here is a diagnostic walk through that will be helpful in covering about everything that could be causing the issue as well as going into more depth about what I mentioned.

Here is the link;

https://www.2carpros.com/articles/engine-stalls