I just checked out the video of your car on the track. That thing sounds great!
I've heard both the GT500 and the KR.
The GT500 has a pretty decent sound to it when you rev it up but I do like the sound of the CS6 A LOT.
The KR sounds unbelievable though
I work at a dealership and we just got a few of them in (KR's that is). They're really nice, but really expensive for what they are.