Yes indeed you are right! the Emotisounds feature is limited to Built-in Sounds only, therefore the Add+Delete sounds buttons are disabled on this version...
No worries though, we have an item to bring it up to the WLM level of functionality. I don't know when but it will eventually.So keep posted for the next version of Messenger Plus! for Skype, who knows it might make the cut
Thanx for posting!