In the last few years, ''sound bars'' have emerged as viable alternatives to traditional six-speaker surround-sound systems. These single speaker units — like the Polk Audio SurroundBAR 360-Degree DVD Theater we tested — employ high-tech wizardry to fool your ears into thinking sounds are coming at you from all directions. Setup was a snap; within minutes, I was ready to listen to some movies. Right away, I was impressed: The sounds were distinct and robust, superior to what I'm used to on the inexpensive 5.1 system I purchased three years ago. And if I didn't quite experience the promised 360-degree environment, I was pleasantly surprised by the sonic clarity, even in lower frequencies. The Polk did a superb job of handling the first 40 minutes of Cast Away: The dialogue was clear and natural, the explosions rattled a nearby window, and the pounding surf had me constantly looking over my shoulder. Anyone wanna buy a used surround-sound rig? A–