Not a video but link below is thread on babybmw website with recordings of my car [HFC DP + MPE] and his car - HFC DP and BCS cat back exhaust which has boost activated powervalves, which he'd shimmed open.
http://www.babybmw.net/viewtopic.php?f=74&t=65935
BCS YT site has plenty of videos of their powervalve exhaust for Mx35i - plenty of folk here in the UK have them.
https://www.youtube.com/user/BCSAUTOMOTIVELTD/videos
Enjoy !!!