I just went through the same situation and thought I might add a small piece of useful information.
For context I have a 2015 f82 m4 with high flow catted (400 cell) turner motorsport downpipes, turner mid pipes and turner valved catback exhaust. Turner told me there is a 50% chance that the high flow catted downpipes would throw a check engine light (from my experience and talking to others, it is 100% chance it will throw a check engine lol).
The spacers/defoulers unfortunately will not fit with the turner catted down pipes just with how the cats are placed- its too tight.
My next next option was to get 90 degree mini cat adapter. Here is the link:
https://drifthq.com/products/pro-spo...sor-cel-fix-91
I read on this thread that you could potentially leave your car tuned to stage 2, turn on the catalytic monitor and with the mini cats you wouldn't throw a light. Unfortunately, that was not that case. I went through 3 drive cycles and every time my check engine light would come on. It was not until I flashed back to the stock tune with the mini cats that I was able to pass inspection.
Moral of the story- I would recommend flashing back to your stock tune even though folks said it is not needed.