If you change any section of your audm exhaust system to a jdm part, you need to either get some custom work done, or replace the rest of the system with jdm parts. The only piece that is excluded from this is the axle back which is the same on the audm and jdm exhaust system.

^^I'm not sure how you got the 5zigen headers to fit. Is 5zigen an American brand? That's the only way I could see it working