I did it a couple years ago with an iPod Nano, using a simple mini-plug to stereo RCA cable that I hooked to a spare stereo analog input. If I remember correctly, I turned the volume up to around 90% or so of maximum. As for the sound, it's clearly lossy compression via the headphone jack's mediocre DAC - but it worked fine for background music during some event we had going on at the time. Audio performance may be better using a docking port, especially if it allows a digital audio output so that you can rely on the 990's DAC.