So you plan to simultaneously playback, record and process live all using the same computer? And to do so via USB with a ZED-24 which only supports two outputs selected from Main L/R pre-fade, Main L/R post-fade, Aux 1/2 or Aux 3/4 and returns to Stereo Channel 3 L/R?
For recording and playback you could probably set the USB output to Aux 1/2 (pre-fade) and use that for recording and use Stereo 3 on the ZED-24 for the computer playback. For adding effects you could select the USB output as Aux 3/4 (post-fade), use Stereo 3 as your effects return and then be sure to not run Stereo 3, the USB playback, to Aux 3 or 4, although you will still have the potential latency issues that TJ noted.
However, because the ZED-24 only supports two paired outputs and one stereo return via USB then I'm not sure how you might approach simultaneous playback, recording and live effects via the USB connection. If you used your M-Audio interface then you might use it for the recording and playback and use the console's USB connectivity for the effects send and return (or vice versa) if the computer supports it.