Subaru Impreza 2008 has resistive steering wheel remote controls.
It can be connected directly to CarPC JoyCon EX.

This links will help you to install CarpC JoyCon EX for the steering wheel remote controls of Subaru Impreza 2008

http://www.subaruforester.org/vbulletin/727950-post61.html

http://www.subaruforester.org/vbulletin/f77/installing-stock-steering-wheel-audio-controls-69816/#post773906

http://www.iwsti.com/forums/gr-i-c-e-security/133987-2008-stereo-install-wiring-diagram.html

http://forums.nasioc.com/forums/showpost.php?p=23485534&postcount=21

http://forums.nasioc.com/forums/showthread.php?p=10308972&postcount=11

http://legacygt.com/forums/showthread.php/supermooses-audio-install-picture-heavy-93803.html?s=842e025d22dd2f65f6e1d9598b822673&t=93803

http://www.scoobymods.com/wrx-steering-wheel-impreza-t127.html?s=b6c5b021250bbd49cf4ca2e7c482a5f7&p=18882

http://www.3gwrx.com/forum/index.php?topic=5082.0