I can't find any reference to a Sunn product named "M6". There was a Model 6 PA speaker with 1x15 inch woofer and a horn in the 79 and 82 catalogs. Probably not worth much unless they are BMWs. (Sports sedan or convertable with a V10 engine.)
If the woofers had a foam suspention, that can be replaced for less than the cost of a recone.