Apple PC Compatibility Card - Manual (Page 17)

17 Installing the Card in a Power Macintosh 4400 or 7220
Connecting the Sound Out cable
16 Plug one of the other audio cables into the connector near the DRAM DIMM slots on the
Macintosh logic board.
You unplugged the original audio cable from this connector in step 13 (the
connector may be labeled “CD AUDIO” on the logic board).
You can use either remaining audio cable. Insert the cable’s larger plug into
the connector, and route the cable through the opening, under the support bar,
and over the top of the PC Compatibility Card.
Route the cable so that it passes under the support bar and through the opening.