Chances are, you'll need an 1/8" stereo - to - 1/4" dual mono Y-cable.
That's right, and it takes care of two problems:
- Splitting the stereo into two monos, since all the UB802's input connectors are mono. The stereo channels of this mixers simply use two connectors each, one for left and one for right.
- The mixer inputs are balanced. You should be able to get sound out of them by feeding an unbalanced signal using a TS (tip - sleeve) connector, but passing a stereo signal on a TRS plug could, in theory, lead to no sound due to cancellation of the two signals. The mixer would consider a perfectly centered signal (i.e., same signal on left and right) as noise and remove it completely.
The other problem is that the headphone output is a little hot for a line level signal, because it's already been amplified to drive the headphones. Using a very low volume on the iMac and lots of attenuation in the mixer may lead to useable results.
recordme, I'd get a cheap Y-adapter like cschreppel suggested (such as
this one) and give that a try. If that doesn't give you good enough quality, a (big) step up would be an etxernal audio interface for your iMac with balanced line outs.
- Martin