Paul, on my A55, Amel installed the Webasto Thermo Pro 90.  It warms up the boat nicely and quickly.  Given that your boat has less internal volume, I would think the 9 KW is enough. The heat exchangers are Kalori Silencio (in the heads) and Silencio 2 (in the salon and the cabins (if I recall correctly).  The Silencio units have a second, booster speed which is very nice.  I attach some materials for your reference.  I hope this helps.  Cheers Joerg  

Joerg Esdorn
A55 #53 Kincsem
On the hard in Vigo, Spain