SF EXTREMA vs SF Cremona M

The Extremas are worth 5000.
There the best monitors i'v heard.
But they need a really powerful amp or mono blocks to sound best.
My friend is using two Meridian 557 amps bridged on the Extremas.
The Skaaning midbase on the Extremas is a Carbon Fiber Polypropelene midbase. This is the best sounding midbase I ever heard. It has a richness and imaging that no other midbase has. I like it better then the new Skaaning midbases which are 100 percent Polypropelene.
The Extremas also use the Dynaudio Esotar tweeter which is a great tweeter.
I would keep the Extremas.

I got another offer to swap SF Elipsa to the SF Extrema then I have to add cash. Is that an upgrade? If yes; how much should I add? Hope to get more advise ... thank you

The common denominator here is that SF enthusiasts want your Extremas and are willing to trade current models to get them. I'd be very cautious about giving them up.

I've heard the Cremona Ms and love them, but based on what I've read, the Extremas have almost another octave of bass extension.

There's someone on Audiogon right now selling the Extremas for 9250$. He's definitely overcharging, but you can see their worth.
http://app.audiogon.com/listings/full-range-sonus-faber-extrema-with-stands-shipping-cartons-beautiful-2013-01-25-speakers-37876-sevierville-tn

Still considering the Elipsa, Extrema option. Cremona is out. Thank you. Hope to gather more advise.

What is it about the Extrema that makes you so eager to trade them?

Elipsa's vs. Extrema's is a very interesting trade. If you need a speaker with more ability in the bottom end, I would go with the Elipsa's. However, not at any kind of uppricing.
OTOH,some of this would depend on the condition of your Extrema's.
You would be trading a speaker with a better mid and high freq driver for a speaker with a more modern design and as previously stated a little more bottom end drive.
Like Donjr asked, what is it about the Extrema's that makes you so eager to trade....IMHO, they are one of the best speakers that SF made.

Keep the Extremas. You'll definitely regret it if you let go your Extremas. I have owned them for 15 years and they are still as good as any modern designs. I drive them with the Gryphon Mephisto. Preamp is the Burmester 808mk5. I use a pair of Townshend supertweeters as well.

Ken Kessler calls them "stuff which legends are made of"

It seems that more are in favor of the Extremas. I might just be looking for something newer & fresher look. Maybe bec. I've had the Extremas for around a decade already, or maybe the itch to change equipment from time to time just like most audio enthusiast or audiophiles that I meet.....I am kinda set to go for the Elipsa but feeling guilty to let go of the Extremas also grrrrrrr....I plan to play around with the KAV300i and Synthesis Magnum 100 which I can't use with the Extremas though...currently using FPB200 which takes more time to warm up as compared to the 2 integrated amps I mentioned above. Regards to all!!!