Sure you can use downpipes, right after you execute an N54 swap.
This piece is just a fix for N54 guys running catless downpipes. It tricks the system into thinking everything is normal with the oxygen sensors. Should work on our cars but consult BMS. I know the same concept won't work on the N55 for some reason.
FWIW, I predict 12whp peak and +20whp above 6000rpm once these are on the dyno.