I don't know what you mean by "clipping headphones", but if we're talking about clipping amps then all is just fine with the Benchmark. AHB2 has 3 sensitivity settings:, 2V, 4V and 9.8V (balanced). Whatever the general recommendation might be (which is fine, BTW, as all standard balanced outputs should provide 4V output), just use the AHB2 with the input that corresponds to the output voltage of your source. It goes without saying that if your source can not provide 4V, you would not use it at 4V setting, but at 2V setting. Nagra Classic DAC would not bring the AHB2 to full power, as it will be 3dB short of that at 2V setting. In studio environment is not unusual to run 20V signal lines as what cables pick up with hum and buzz is your noise floor and having a high voltage signal increases your S/N ratio. That is why AHB2 has 22dB level input and if your source can deliver that, it should be used at that setting to decrease the noise that's picked up with cables.