I have a 2kW Airlink BMU and it offers a considerable improvement in tone/texture/detail etc, but it did somewhat 'go off' after a while. Out of curiosity I replaced the SL32 surge-limiting thermistor (the big black disc thing) with a new, identical component and the magic came back, in an instant. So, this leads me to suspect that these BMUs are probably better off with a proper 'slow start' circuit, such as the one that Sjostrom Audio sell as a bare PCB, to limit inrush current, rather than a thermistor. Sadly, there is no room in the case of my Airlink BMU for that circuit.