I would imagine that like all quality speakers the crossover for the RM1 is optimized for the specific drivers, so I would recommend simply getting the woofer(s) refoamed. Of course Brian is final say on this, but I’ve been a DIYer off and on for years, and I can’t imagine you’re going to be able to replace the woofers without noticeably changing the system sound. In fact, I would suggest that either get Brian to refoam them, or at least have him supply the surrounds, because all surrounds are not alike.
I have a pair of these and they are definitely worth the effort to get them back to Brian’s specs.
Good luck.