To me at least, I find that it changes the timbre/colors the sound. Just trying it now with the andromedas, for example, vocals sound a bit dryer, slightly more nasally, and lose their euphony for me. Timbre feels off, especially in cymbals, and treble feels hot/harsh to me. Even though I know it's really just a resistor, I don't like how it sounds... I've found I always prefer listening with no IEMatch than with one across multiple amps with the andromeda (it's why I like the es100 so much, I don't need an IEMatch to listen with the andromedas). But judging by the many positive impressions of the IEMatch I've read, I might be alone here.