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:

1. Download and unzip this package: CirrusAudioXP_Macbook_c.zip 1.0.0.13c (Nov. 1, 2009).
2. 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.
3. Reboot.

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