I'm surprised you don't like the FI exhaust. I just installed mine last weekend but maybe you're not liking it because you're running the long tube headers instead of the stock cats. Did you get yours with resonators? Sounds like no
I got a clip of a dead stop, no launch to wide open throttle which I love how it came out
https://www.youtube.com/watch?v=7V0Kav24OLs
This is with stock cats, waiting on my motordyne art pipes