Step 5 - Playback From Itunes - Apogee Symphony I/O User Manual

Apogee DA8-IFC
Connect speakers to the rear panel analog outputs 1-2 using an
cable
or equivalent.

Step 5 - Playback from iTunes

After restarting your Mac, a dialog box will prompt you to choose Symphony 64 for Mac
sound output. Click Yes.
Open Apple iTunes and play an audio selection.
Using the front panel left hand encoder, select the speaker or headphone icon; use
the right hand encoder to adjust the playback level of the selected output.