“I am now happy. Happy with the KMix version shipping with KDE4.11. Happy that I can now declare Media Play control as stable.”
You might neither be surprised or impressed or as happy as I am now. Here is the explanation: For years I mainly maintained KMix for following up with changes dictated by the outside world. The last year was very different and awesome – last year’s KDE Randa Meeting brought enough motivation to do critically needed KMix refactoring, and add support for media player contol (MPRIS2). KDE4.11 stabilizes the media player support. It is now really smoooooth.
Enough talking about me, and back to you, the user. Integrating media player control (MPRIS2) was dramatical harder harder than I anticipated. Issues arose where I did not expect them. I sincerely apologize if you endured issues, hangs during start or running the KDE Desktop due to KMix. Please go for KDE 4.11. All will be well now. If not, let me know.
I thank everybody involved, especially apachelogger for practical advice and Albert Astals Cid for coping with me technically being too late for KDE 4.11.
 Well, I guess that everybody reading this is a KMix user. But not the other way round.