We just did the same upgrade to our shop 550i. I know the Dinan parts are very expensive, but they work well and bring this car more in line with the F10 M5. But I agree and am surprised no other tuners are getting into this car. The Dinan upgrades have transformed the car and as stated, remains incredibly smooth.
I heard a rumor that Dinan will be offering turbo upgrades along with Intake and oil cooler upgrades.