fozzy, the KS 10 I isn't a complicated piece; it's just a straight-through extension cable with Binder plugs on both ends.
I'm not sure exactly how the inputs to the Lemosax are set up, but you should be able to test the same setup without the extension cable, no? If that works, but then it doesn't work again when the cable is used, the cable needs repair. That should either be free or cheap, depending on your warranty situation.
--best regards