+1 on Smudge's comment above. It's a lovely sound - loud, but not annoyingly so (Unless you're a track marshall at Castle Combe)
This centre pipe won't fit your K2,it's a different shape. The point where it meets the back box is different. I've just had a 3 inch stright thru centre section made for my K2 and it hasn't made it much louder due to the chambered construction of the back box. Sounds nice, but not much louder. I imagine the Nismo is much less restrictive, hence adding the straight thru section on this would make it louder as Smudge said.
GLWTS mate.