When someone says a piece of audio equipment is a sleeper, he means it's generally thought of as a better quality piece, but one that's not talked about a lot therefore does not sell for a lot of money because people don't know a lot about it. At least that's what I've always thought it meant. Like this Mitsubishi amp is not that well known but it very well constructed, performs very well, looks great and doesn't sell for a huge amount of money. Since I sold my VRD-ST45, I've been using mine with my Blueberry Extreme II and Klipschorns and it sounds great.