Dude, where’s my bass?? Ah, stiffened rubber surrounds, who knew?

Started a thread on “Cables” re: better cables to help restore bass to my B&W CM-4 speakers...so, while preparing speakers for evaluating assorted cables, our daughter - who has very acute hearing, unlike my senior ears! -  noticed sort of a “ crackling”sound in left speaker, and sure enough, removing cloth speaker covers, we noticed a 6cm hairline fracture in the surround of the mid-range cone.  In fact, checking the rubber surrounds of bass and mid-range speakers in both speakers, there were significant areas of stiffened and brittle rubber material, which - I would presume - drastically muted the speaker responses to incoming audio signal.  So, what to do?  Can the surrounds themselves be replaced w/o impairing cone sonic qualities?  Totally new area for me, having never dealt with material deterioration in speaker components.  Suggestions most welcome.