I've upgraded my ix2-200 (FW 2.x) to cloud edition a long time ago and sucessfully by carefully following theses instructions:
http://blog.millard.org/2011/09/iomega-ix2-200-nas-non-cloud-to-cloud.html
For the ix2-200, FW 3.2.14.30167 is the latest. v4 will not run because of HW changes.
At your own risk, of course!
As a side note, I did not really like the 3.x firmware. The new Twonky version did not allow anymore to use the 'Album Artist' field instead of 'Artist', which basically screwed up how my huge music library was displayed. It also added a lot of useless stuff (I'm using it basically as a DLNA server fo music, photos and movies) so YMMV.
