That’s a logical, but potentially faulty, assumption on your part, but, okay. Let’s grant that the input signal to the effects-box is absolutely perfect according to the standard audio measurements, THD, noise, FR, etc. - I’ll leave aside for the moment, the fact that the objective performance of electronics has long since surpassed human hearing acuity. So, by definition, the effects-box is altering the measured objective perfection of the input signal in order to produce a playback which sounds significantly closer to the original live performance. Would you accept such playback, or would you reject it because it altered the input signal to achieve that?No, because that effect has made a compensation for an other fault in the system.
We come full circle. Which type of system performance is the most important? What is the ultimate purpose of a music reproduction system? Is it to satisfy spectrum analyzer measurement, or is it to reproduce music which humans find perceptually indistinguishable from original live event? Once you come to grips with answering that question to yourself, you can let go of the intellectual trap of concluding that a perfect signal transfer path is the most which can, or should, be aspired to for a playback system. Yet, as I point out above, the signal transfer path (short of the speakers) is effectively already perfect because it well exceeds human hearing acuity? Achieving THD that’s double-digit zeros to the right of the decimal point will not move the music as sounding any closer to the original live event.Only system performance matter. Boxes, and their (clinical) performance are irrelevant…