That's very true, but the pro audio community usually thinks nothing of putting all kinds of things in the signal path for the convenience of manipulability, and are often looking for pleasing colorations rather than maintaining ultimate transparency. IME, you can hear an additional solder joint, let alone a volume pot, active circuit, tube or transistor, coupling capacitors, resistors, etc.. Just because they have already been used in the signal path of the recording, mixing and mastering doesn't mean they wouldn't further degrade the sound. The question is whether what you gain from the device is worth the degradation to YOU. There's no question the Manley EQ is a good one. There's also no question that you could hear its presence in the signal path on a resolving system with its settings set to flat. Some may remember the EQ offered by Cello about 15 years ago, although I believe that was marketed primarily to make EQed recordings iistenable rather than to correct for the room.