I had the Zumo 550 with the XM30 and I now have the Zumo 665 with the XM40. I'm going to go out on a limb and say that the XM30 is for the 550 and the XM40 for the 665. I do not think they are interchangeable. The 665 is able to do more like get nexrad radar which I assume the XM30 wouldn't be able to bring in. All of this of course is just a guess on my part.