Different components typically provide very different levels of accuracy. Many amplifiers and DACs are all but transparent, whereas speakers and turntables normally fall quite far short of transparency.
I don't know if allowed, but I'm going to say that the product which has most profoundly improved my system is the tone-arm which I developed. It has transformed the accuracy of my Amadeus, my Garrard 301s, my Technics SL-1210, my Linn Sondek and my cartridges. For the first time I've heard my decks blithely sail through torture tests on opera or very hot pressings with an almost digital accuracy. With some fairly common cartridges it can just about track the fourth Hifi News tracking test, which I think does give a little insight into the performance available at the most difficult peaks of many records. The stability, dynamics, revelation of detail and acoustics, separation of tones and instruments during complex compositions, access to harmonies, width, focus and depth of soundstage, and sense of physical presence are all unprecedented in my system.
Of course, I have no credibility in saying this about a product which I myself offer, but comments from others which are beginning to appear on the forums suggest I'm not alone. Several users seem to agree that their decks are reaching new levels of performance.
I could have appeared more honest if I had chosen a product other than my own, which would have been one of Creek OBH-22, active Linn 242s, Well Tempered Amadeus.