Sport Exhaust Group A?

This is about modifying the exhaust system on my Audi A4 B5 AFN.
I'm not entirely sure what changes I want to make to my exhaust system yet.
to ensure that the back pressure in the exhaust system remains as low as possible after the turbo, because the exhaust flow has increased enormously due to the tuning, and the exhaust pipe already whistles at full load. No joke.
Here are some options I'm considering:

1. Remove "Kat" (in all variations).
2. From category A or N, depending on the specific requirements. I'm not familiar with the difference between these categories (expensive).
3. Single-exit exhaust muffler only.
4. Sport exhaust muffler with replacement pipe for the center muffler (likely a bit loud).
5. Or, simply a modification of the stock muffler. It's practical: remove the inner part and weld it back on.

"Has anyone here had experience with the A4?"
Can anyone tell me if the original center muffler is an absorptive muffler?
When it comes to Entopf, I know that it is a reflective sound absorber.