I have worked with Joel Rapose and know him to be a stand-up guy who is helpful to BMW riders. His website is self-explanatory. The system once known as MZ-B was bought out and is now called PowerDynamo. There have been many changes since I last worked with the system.
Vech’s system is also quite good. Learn which will suit your purpose and budget.
Both systems can be converted back to “original”, should the desire arise.