I've been following this thread from the beginning. Your case of finding the M3s "sibilant" is so bizarre and atypical that I've asked that your M3s be checked out in our lab when they arrive from our Michigan depot. They are expected today.
I regret the errors in the finish as well as the broken logo for the replacement pair. As you know we will stand behind the product. IN all my years with Axiom (8), no one has ever described the M3s as sibilant, which makes me think that there may be a defective woofer in the original pair you got (unlikely, but possible). I'm worried there is something very wrong in your setup.
Anyway, please listen to the replacement pair of M3s. They truly are a really fine speaker, more natural, neutral and pleasing than many high-end 2-way bookshelf models that sell for $2,000 per pair.
Axiom Resident Expert