Old info possible but.... may work with Windows 8 or have new drivers (definitely), shame that Boot Camp 5.x package leaves things out still I guess.
MacBook Pro audio sound fix
http://realitypod.com/2010/07/macbook-pro-no-sound-in-windows-7-final-fix/
Cirrus Logic CS4206A (AB 11)
I tried downloading the "High Definition Codecs" driver from Cirrus Logic's website but the download link doesn't work.
http://www.cirrus.com/en/support/lic/lic3.html?uri=/en/pubs/software/CS4207WinVi sta_Win7_32-64-bit6-6001-1-30.zip
In macbook pro, you may also see a red light in your audio jack. *Step 1:* Download the Macbook Pro Cirrus Logic CS4206A Driver from our server.
+(As a request, please do not hotlink this file anywhere else or our server will automatically remove the file from server.)+ +In case the above download link does not work google+
CirrusAudio.10.6.1.zip
*Step 2:* Extract the right type of Driver (depending on your windows XP/ 7/ 32 bit/ 64bit)
Step3: for Windows 7 only: Right Click on exe file of driver. Select Properties> Compatibility > run in compatibility mode Select Windows Vista from drop down menu and Click OK
*Step 4:* Double click the driver and install.
MacBook Pro Cirrus Logic Audio device driver
http://www.lonare.com/topic/230/macbook-pro-no-sound-in-windows-7-solved/