I had mine check with the BMW warranty dept on things I've done. Basically any issues caused by the installation of an aftermarket part is your problem. I've had it confirmed that an after market exhaust is no big issue. The ECU is another story and no matter what anyone tells you, BMW will know it has been tampered with.
I have allot of faith in CA and have ordered a few things through them. I find they are always honest and one of the few companies you can trust to deliver. If I was going for an aftermarket ECU I would go with them and only them...
Do you have any other mods, reason I ask is that there are many other ways to improve the performance and an ECU remap may not provide the best solution. Changing the suspension and brake set-up will probably give you a much greater advantage than a ECU remap.
I do recommend the RPI scopps and BMC filters which you can get from CA.