What unit are you referring to?
On my Furuno GP7000 and on the 585, there is a menu prompt for either 600 or 1000 watt output. You can use a 1000 watt transducer on a 600 watt sounder but you can't use a 600 watt ducer with a 1000 watt sounder
As far as transducers go, Airmar is the manufacturer for most if not all of Furuno's transducers.