If your bootcamp windows is having very poor volume output on 2009 unibody MacBook Pro, here's the solution: http://www.stuffedcow.net/macbook_audio. Thank you, Henry.
I follow the instruction below, plus a reboot, and fixed the problem:
- Download and unzip this package: CirrusAudioXP_Macbook_c.zip 22.214.171.124c (Nov. 1, 2009).
- In Device Manager, Update Driver for the Cirrus Logic High Definition Audio device. Don't let Windows search for or do anything automatically. Manually choose to the driver from a list, and use the "Have Disk..." button.
My configuration is latest 13" MBP (MB990LL/A), bootcamp 3.0 from Snow Leopard, and latest Windows 7 (build 7600).
The detail discussion can be viewed here: http://discussions.apple.com/thread.jspa?threadID=2037093&start=449