This is an older legacy cable, it was used to connect the audio output rom the GS-1100A to the older iPhones and iPads with TRRS jacks. 

If you are handy with a soldering iron, and want to save $25, then you can find instructions on our forum here;

http://www.gammaspectacular.com/phpBB3/viewtopic.php?f=15&t=255&p=1184

Cable length: .......... 50 cm

Resistance: ............. 1 KOhm

** Note: No special adaptor cable is required for the GS-USB-PRO, it connects to a headset jack with a standard TRRS to TRRS cable **