My setup consists of FI resonated HFC's and 18" resonated exhaust... the sound is PURRRRfect. Roars like a lion when I hammer the throttle, purrs like a big cat in regular driving, and quiet when I want it to be. BTW, I think you should hear Tony @ FI's recommendations. Back in 2012 when I purchased my system, I described what I want to hear, and he recommended a setup, and he was Spot-On!
Here's what I wrote about the sound of my FI system back then:
Fast Intentions exhaust is here!