A necessary device is one without which there is no music. Products like QOL, or in this application the AntiMode 2.0, are not necessary. They may be perceieved as enhancing the system's sound, but their removal does not halt it.
Now, if the AntiMode 2.0 is used as the preamp then it becomes a necessary device, assuming the source has no attenuation.
Now, if the AntiMode 2.0 is used as the preamp then it becomes a necessary device, assuming the source has no attenuation.