maye check microsoft for an update to the game? i know there's suppoedly an issue with the audigy 2 zs card and the OEM version fo halo that ms has an update for or soemthing. maybe try that?
Just bought a new Sound Blaster Live! LS card so I could utilize the EAX feature during Halo. As you may know, in order to enable EAX in Halo, the user must first enable Hardware Acceleration in Halo's Audio setup. However, enabling Hardware Acceleration in Halo causes the sound to cut out. I did a Directx diagnostic (version 9.0) and received the feedback that my card does not support hardware buffering. That's the whole reason I got this card!
Creative hasn't been much help either. There website doesn't really say much about hardware acceleration. They seem to focus on the fact that their cards all support EAX, but they rarely mention the hardware acceleration issue. I did find ONE comparison chart where they compared the Audigy series with the Live! series and they put "N/A" next to the entry for "Hardware Acceleration of EAX &/or EAX ADVANCED HD" next to the Live! card.
It looks like the least expensive card that supports hardware acceleration is the Sound Blaster