After reading your comment:
"I just want a LITTLE bit more sound coming out of this thing but I don't want it obnoxiously loud and definitely don't want any drone"
I wanted to let you know I too did an "exhaustive" amount of research into upgrading the OEM system on my 2011 550i, and came to the conclusion that the DINAN product for our car was the best choice for me.
I had their free flow exhaust system installed earlier today, AND I LOVE IT! It's very classy at idle (sounds just a bit louder than stock, but way smoother and more menacing), but really comes to life when I toe in to the accelerator pedal. I drove around town for a bit after installation with all of the windows down, and really enjoy how it sounds. I then got on the freeway for the drive home, and with the windows up and radio off, there's hardly any increased drone over the OEM set up (just a bit around 2,000 - 2,500 RPM, but in no way offensive or obnoxious).
Step on it for some aggressive driving, however, and you'll know without question that you're not running stock...
Plus, the laser-engraved quad pipes look fantastic too!
I know there were cheaper options out there to consider (as well as a bunch of more expensive ones as well), but in the end, I think I made the best choice when it came to getting a greatly improved exhaust note without having to deal with increased cabin drone. The DINAN set-up maintains the valved system as found on our OEM exhaust, but does a much better job at producing a healthier and much more pleasing sound without being too loud or offensive (which is exactly what I was looking for).
Hope this helps...
