I am currently running the 27KX in my car. I can honestly say it is the best sub I've used so far. I have it in around a 1ft^3 box getting about 400 watts RMS from an Alpine MRV-T757. Without a doubt the most accurate sub I've used. It is far from the loudest (but I wasn't really looking for loud when I bought it).
Well the reason I ask is because I have the choice of the kx and the morel ultimo, I just don't want everyone to chime in and start talking about the ultimo! I know what it does!
But when I search for info on the kx subs info seems to be pretty scarce
Running 33kx, very very happy with it.....Extremely accurate and dynamic. For more output, ask Mr Nick Wingate for a ported enclosure design. Using the same design , plays flat, very low extension and great output.
As I have zero experience with the Morel driver I will not be making a comment on the pro's and con's on it. Having said that let me say this on the KX series of subs. Focal's philosophy has always been to build a "SUBWOOFER" not a bass driver. Big difference!!! Every KX series subwoofer is designed to be as accurate and linear as possible. They are not a "Club Sound" banger, but designed to reproduce as accurately as possible extreme low frequencies. 90% of my IASCA/USACi/MECA competitors use the KX series of sub's, ( 33KX is the most popular choice), and no one has any complaints on the performance of them. They are designed to play in a sealed enclosure, but some of them can be used in a ported enclosure. All of them are very efficient and don't need thousand's of watts to driver them, ( exception would be 46KX4 1000 watts nominal).
My suggestion would be to examine how much airspace you are going to allocate for the sub and look at the appropriate KX sub and see if it meets your needs. Seek out those folks who have one or better yet go to your nearest Focal dealer and see if someone there has installed one or has actually purchased one and listen. Its the best advice I can give you. Your ears are the best judge as to what works for you!
Hope this helped!
National Training Coordinator