Advice on replacing 12 in woofer in Martin Logan Monolith III's


I'm needing to replace the 12 inch woofers in my Martin Logan Monolith III's.  I am running a dBx 260 active crossover so I can control x-over points and output.   Any suggestions? 
stevepa
Even though the post was a year ago
My friend contacted him only 3 mts ago, still had them.

Cheers George
The MMS of the 30W/4558T00 is the moving mass, it’s some 36g higher/heavier than the SV-12 which says to me it’s not going to be as good at 130hz and 1 octave above, fine for below 80hz but the Monolith panels won’t take to that low frequency too well.

Cheers George
That's good news!   Hopefully he will respond to my inbox.  Thanks for all your help George!

just ran curves on the SV12 in 3 cu ft sealed.... It'll be 3db down @ about 31 hz with a qtc of .79
Thanks for the info Tim.   Finding that driver is the problem  :).  It seems they are very hard to come by so I'm trying to figure out what the next best thing is.