I also use that term to describe a sound with less tendency to "bloom" along with the dynamic transients. It certainly doesn't mean reduced dynamics, just more stability.
The antonyms could be "forward" or "aggresive". A "laid back" soundstage would extend behind the line of the speakers. A "forward" soundstage places some imaging in front of the line of the speakers. "Aggressive" can be like jumping out at you and slapping you in the forehead.
The most "laid back" amp I've found so far is the Plinius SA100, which is very capable but doesn't try to impress. The tube amps I've tried tend be a bit more forward. The most aggressive amp I've had was the mosfet-based Mission 777, from the early 80's, which was a lot of fun in a masochistic kind of way. Never left any bruises though.
Often, just adjusting the toe-in of the speakers will have a dramatic effect on the perception of depth of the soundstage and imaging.
The antonyms could be "forward" or "aggresive". A "laid back" soundstage would extend behind the line of the speakers. A "forward" soundstage places some imaging in front of the line of the speakers. "Aggressive" can be like jumping out at you and slapping you in the forehead.
The most "laid back" amp I've found so far is the Plinius SA100, which is very capable but doesn't try to impress. The tube amps I've tried tend be a bit more forward. The most aggressive amp I've had was the mosfet-based Mission 777, from the early 80's, which was a lot of fun in a masochistic kind of way. Never left any bruises though.
Often, just adjusting the toe-in of the speakers will have a dramatic effect on the perception of depth of the soundstage and imaging.