Urei 813c or 815c to have a listen first.
If i do not find one i guess i will go with the JBL 4350/4355
OK if you like them great but none of them are supported so if you loose a driver and need to re-cone. You are out of luck.

Both the E-145 and 801C usable for the coaxial 15 in the 811/813/815C are long gone so are the LE-15's. The earlier Altec's coaxial s might be fixable through Great Plains. The helper woofers in those would also not be OEM re-cones.

The 4350/4355 no woofers re-cones might get luck with 2235's but can't depend on it and no 12" 2202

I don't know why you don't try a sub with what you already have might save you some money in the long run.

Well in any case good luck hope you find something you like.

Rob