iTunes Audio Configuration problem dependent of logged-in User

Dear all,

I'm desperately looking for a solution to the following problem. Spend hours and hours "googling", but found nothing that solved.

Problem:
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Have a 4 year old family PC (multiple user accounts), WinXP Home SP3, had to change the motherboard (ASUS P4P800-something, fysically damaged)) to one (ASRock P4i65G) with different chipset, audio etc.
Now everything, including sound works fine on all (!!) user accounts.

iTunes however only works on 1 (!!) user account ("userA")! For all other accounts ("userB", "userC") the message "iTunes has detected a problem with your audio configuration. Audio/Visual playback may not operate properly."
All accounts are "administrator" accounts (full rights)


Configuration:
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Motherboard: ASRock P4i65G ( http://www.asrock.com/mb/overview.asp?Model=P4I65G)
On Board Sound: Cmedia 9761A 5.1 channel audio codec, driver version: 5.12.1.49

Device shown in Windows: C-Media AC97 Audio Device
Windows XP Home SP3(upgraded from SP2 after problem occurred)
All accounts are "administrator" accounts (full rights)


History:
--------
1. Replaced motherboard (no chance to do anything before, MB was damaged during installation of a PCI-card)
2. restarted PC as "userA"
3. XP recognized new hardware, installed driver for it.
4. No sound
5. found about "hidden devices" and environment variable "devmgr show_nonpresentdevices"
6. using above, removed old (SoundMax) driver.
7. rebooted ("userA")
8. Everything (including iTunes) works fine for "userA"
9. Sound works for all other users as well, but iTunes continues to complain and doesn't give any sound.


What I did (please don't advice again):
---------------------------------------
1. Updated C-medai Audio driver to version 5.12.1.49
no change
2. a. Uninstalled iTunes and QuickTime
b. rebooted and re-installed iTunes+ QuickTime (Apple recommendation)
result: nope
3. a. Uninstalled iTunes and QuickTime
b. Uninstalled Audio device from Windows (Properties, Hardware etc.)
c. rebooted ("userA")
d. updated C-medai Audio driver to version 5.12.1.49
e. re-installed iTunes+ QuickTime
nothing changed

Several of above mentioned actions repeated several times to be sure...

_Thanks in advance_

Every tip (except what I already did) is very welcome, I'm desperately looking for a solution.

best regards,

Hans Troost