The more highly resolving the system, the bigger differences smaller improvements can yield. DACs, along with every other piece in the system rely on the overall context of room, cables, isolation, etc. The insertion of a new component can illuminate what the context provides as well as showing its own character. Does the component in question provide new and deeper insight into the soundstage? Does it offer finer resolution of timbres and decay? Does it reveal something that was previously hidden? In my experience when these things are happening, the experience is usually deeply satisfying and an indication that the surrounding equipment provides a beneficial context.