Essam originally used the Pioneer because it only required a small enclosure, and several of us can attest that it does indeed work. If the Fosgate uses the same volume of enclosure, then I am sure it is a quality product and will be just fine.

Not sure what you mean about tweeter replacement projects. Many have replaced the originals with BSW units with great success. Others can be made to fit with the usual fabrication.

Just be aware that BMW uses a system that sends specific signals to each speaker, so you have to be careful if you update them. Even the most expensive and exotic tweeter might not necessarily sound good just hooked up like the original.