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

Hi guys,  sorry on the Peerless recommendation, I don't know why I missed that it was 83db sensitivity.
@stevepa    on the Peerless SLS 830669, it will go down to about 50 hz in a sealed box. I would not mind porting the box on the right driver, but this driver really wants a large box ported. Also, it has a very cheap frame. That does effect sound quality.
In 3 cu ft, the Scan Speak will work well. The Monoliths published crossover point is 125hz. I believe stevepa said that he was crossing electronically. Good excursion limits, however, with a qts of .32, you must vent or port your box with this woofer. If you do so, it will go be 3db down at just about 27 hz in an sb4 alignment or 24 hz in a qb3 alignment.
As it stands, I'd run this way without worry of distortion.
Of course box size could change it all. 

Just thinking,  if you are using electronic crossover and biamping, why do we care about matching sensitivity or impedance? 
I still think that 83 is too low, you'd have to drive it pretty hard to keep up,  but you could certainly use anything from 4 to 8 ohm from 87 to 92 sensitivity. 
Based on that, I will expand the search.

you must vent or port your box with this woofer

The Monolith I was ported and the bass couldn’t keep up with the speed of the esl, that why with the II and the III they went sealed, tighter faster except they used that junk cheap driver, I posted it’s T/S here.
http://www.martinloganowners.com/forum/attachment.php?attachmentid=18105&stc=1&d=1437711906

The one Jon Fo used could work Peerless 830699 but it’s FS is much higher (double) that of the SV-12
http://www.martinloganowners.com/forum/showthread.php?16441-ML-Monolith-III-and-damaged-woofer&p=173694&viewfull=1#post173694

Cheers George

Thanks for all the input.  I have reached out to ScanPeak  for more data on the Discovery 30/4558.  Also inbox the guy that had the SV12's for sale,  but haven't heard anything. Even though the post was a year ago, I think maybe he still has them.   I will be putting a sub with the setup,  so I don't need it to down real deep.  Question:  what would be the ideal  crossover point for the ELS  running at three-way?

Even though the post was a year ago

My friend contacted him only 3 mts ago, still had them.

Cheers George