I had the exact same issue in our Copmany. Rambling days with it. I opened a HP CASE an got an Answer that worked for me:
1. delete a Regkey: HKLM\System\CurrentControlSet\Services\AEAudio
commandline: reg delete HKLM\System\CurrentControlSet\Services\AEAudio /f
2. Reboot the Notebook
3. Installation HP Audio Driver for the Elitebook 8540w (sp46721.exe)
Audio works now! :-) We can Deploy the Elitebook 8540w with Windows XP SP3.