No sound over hdmi on 5741a

Hi,
ive been struggling all week with this issue.
i installed xp on my acer 5741a (thanks to help from members of this forum), and all is dandy, BUT, the realtek hd audio is driving me mad,

i get sound on the laptop after installing the realtek audio drivers, but try as i might i can get no sound over hdmi (i get hdmi sound fine using the windows 7 install the laptop shipped with).

on xp, during the realtek driver install i keep getting the found new hardware wizard popping up asking for divers for 'high definition audio bus', which i can not seem to install, so i cancel that wizard and get on with the realtek driver install, which goes fine.

after the realtek driver install (and working sound on laptop) i notice some yellow exclamation marks in device manager under 'other devices', including--
audio device on high definition audio bus

i assume its this thats stopping audio over hdmi ?

ive tried to install the latest motherboard_driver_audio_microsoft_bus.exe, uaa stuff etc, but nowt happens, and i cannot seem to uninstall the old default 'microsoft uaa bus driver for high definition audio' that already exists in device manager/system devices in my winxp sp2 installation, i think this is blocking me installing a more recent uaa ?

i had this same issue last year when i installed xp sp2 on msi x410, and despite good sound on the laptop, i never did manage to get sound over hdmi, aaaarrrggghh, why is the realtek hd audio such a pain !

cheers