Have you activated the automatic recalibrated system of your speakers so that the power amplifiers set themselves to the correct power value using the internal software circuit in relation to the speaker microphone. If the calibrated system detects troubles in the hardware it wil let you now with led colors so I read in the user manual.

I read in the service manual that the tweeter impedance should be 6,6 ohm and not 3 ohm as you specify as good !

humm...interesting... The document I found on the internet mentions on page 15 the impedance of 5.7 Ohm for the midrange and 3.0 Ohm for the tweeter. Furthermore, just to record here, 3.1 Ohm for the lower bass and 5.0 for the upper bass. NTC sensor 470k Ohm @ 25oC. Anyway, i just found out that the problem resides in my Beosystem 3. I changed the powerlink port and the problem was solved. I don't understand why...