The digiport is for connecting to compatible digital MP3 players. From Appendix in manual (with numbers in parentheses referring to locations/buttons on front of player as shown in pic in manual)
EDIT to add - though the radio/DVD player doesn't appear on their website (or at least, that I could find), the mfg website is
http://www.rockfordfosgate.com Contacting their support dept might lead to finding where to buy the cable and which MP3 players are compatible. I suspect it's limited to iPODs, but dunno
Reference User Guide for the Digi Port Adapter
(the adapter is sold separately)
1 - connect the adapter to Digi Port (32)
2 - ENTER (28)
when the adapter connects to a compatible digital MP3 player (see dealers for list of compatible players) press this key to enter submenu or to execute a command
3 - MENU (27)
when the adapter connects to a compatible digital MP3 player, press this key to enter parent menu
4 - STOP (26) stop playing
5 - PAUSE (25) pause playing
6 - FR(<<)(12):
short press, jump backwards 10 song to play; long press to fast rewind
7 - FF(>>)(11):
shor press jump forward 10 song to play; long press to fast forward
8 - TRACK +/-(7)
press to select previous/next song
9 - SHUFFLE(22)
short press to turn on/off the random play function
10 - PLAYLIST (17)
short press this key to display the playlist. Turn right knob ("STEP+/-") to select desired playlist. Press "ENTER" to play
11 - ALBUM(18)
short press this key to display album list. Turn right knob ("STEP+/-") to select desired album. Press "ENTER" to play.
12 - ARTIST(19)
short press this key to display artist list. Turn right knob ("STEP+/-") to select desired artist. Press "ENTER" to play.
13 - GENRE(20)
short press this key to display genre list
14 - SONGS(21)
short press this key to display all songs list.