AdvMAME/ArcadeOS sound issues

[JoyMonkey]

I'm running a DOS setup from an old Dell computer I'm
using for a cocktail cab. It uses onboard sound and works
just fine when running regular DOS Mame from ArcadeOS
ie. sound in ArcadeOS and DOS Mame work perfectly.
I've selected SoundBlaster sound in ArcadeOS and default
DOS Mame settings.

However, when I made the switch from DOS Mame to Advance
Mame, I can't get any sound from Mame. I've gone through
every soundcard in the Default Settings for AdvMame and none
work. Setting to Auto will get the games running, but no sound.

I'd like to get the onboard sound working rather than using a
seperate soundcard, as I've got a couple of these computers
that would suit cocktail cabs very well as they are.

Anyone know what the problem could be?

Here's my setup:
ArcadeOS 2.5
AdvMame 0.67
Dell GX1 P3 450Mhz, 128meg
Onboard Ati Rage Pro
Onboard Sound (AC97?)