Ok, I found an other way to become the kegs sing balanced. I analyzed the cable of the jack and found out that there are 4 wires, not only 3 like mentioned above. Thought, that mine is an other version with new cable. Measured the cable against the jack and colored the wire regarding polarity. Then cut the cable. Measured the cable against the kegs - recognized, that there are only 3 wires In use. Damn. Only reason could be, that in the y splitter they have soldered the both ground wires of the cables to the kegs. So opens the Y splitter and resoldered the cables. Now I have balanced kegs singing on my 9038s - wonderful
Was a bit fiddling but worth the work.