Wilson X-1 Grand SLAMM. I never owned a pair, but when I was young and returned home after college I went looking for a new stereo to move into my place with. Knowing nothing back in the late 90's I randomly walked into the first stereo shop I found myself walking by in New York City, which happened to be Sound by Singer. Straight out of college I obviously could not afford anything in there, however a nice salesman let me listen to a few systems, one of which was a pair of Wilson X-1 Grand SLAMM speakers hooked up to full Krell kit. Before that the nicest hi-fi I had heard was my parent's KLH Model 20 stereo and my buddy's Onkyo integrated with some Cerwin Vegas. I never knew that hi-fi could sound that good. So that started me on my audio path.
So, to answer your question the Wilson X-1 Grand SLAMM changed my hi-fi life, because without having heard those, I probably never would have gotten into this stuff as deeply as I have.