Once I first got my hands on Sony's PlayStation Portable back in 2004, I tossed the flash music player that I'd been using in favor of the new gadget on the block. But I quickly discovered that the PSP wasn't exactly a booming system when it came to audio output. For music and videogames, turning the sound all the way up mostly did the trick when armed with regular or noise-canceling headphones. But for video, typical New York subway noises would overwhelm its dinky maximum volume, to say nothing of the engine sounds on a cross-country flight. What to do?