The 4.4i exhaust with dual tips are a direct bolt on.
A few companies make stainless cat-back systems (billyboat, super sprint, etc), but they are pricey.
You can also just take your 3.0i exhaust to a local shop and they can weld on some dual or single stainless tips. This is probably your best option if you just want the exhaust area to look better.
There is or was a company out of Russia called drlavr. They make very high quality headers specifically for 3.0 e53s. Once the war started they stopped selling in the US. Their site also recently went down. So this might not be an option anymore.
Pics of header:
https://www.pinterest.com/pin/170151692164140957/
Instagram page:
https://www.instagram.com/bmwdoctor.ru/
Their (no longer available) site:
https://drlavr.com