Headphone maker Urbanears is expanding its lineup to include the affordable DJ tool Slussen ($15), which allows a DJ to cue up tracks without interrupting the music that's playing, assuming you use a free Urbanears iOS app. Plug Slussen into your iPad, iPhone, or iPod, then connect speakers into the speaker port, and headphones into the headphone port; you can monitor one track while playing another. The U-shaped accessory is small enough to carry…
