For some reasons, we do not support DirectSound directly in the VXD driver. We just have the DirectSound software emulation layer do it for us. I think that is why you have delay in sounds in DirectSound games. We suggest you to upgrade your OS to Win98SE or later versions. Our WDM driver has more powerful features, such as EAX support, and it will support DirectSound better than the VXD driver.
Our AC'97 CODECs support the SPDIF function on P4B with the WDM driver. With limitation of the MS kernel driver, the Win98SE cannot support SPDIF with AC-3 format without MS QFE269601 installed on Win98SE. If you want to play AC-3 format under Win98SE, QFE269601 should be installed. If you want to play AC-3 format under Win2000, service pack 2 should be installed. WinMe and WinXP can support AC-3 format without any patch files from MS. For Wave (PCM) format, all Windows OSes can be played with the WDM driver.
In fact, the AC'97 audio CODEC is a standard CODEC for audio controllers. The most important part is the audio controller which is provided by SouthBridge chipset vendors. We are an AC'97 audio CODEC vendor, not a SouthBridge chipset vendor. AC'97 audio CODEC drivers are varied for different audio controllers. But if the audio controller is the same, the same drivers can be used for most AC'97 audio CODECs. If you can find drivers for your audio controller for the other OSes, they can usually be used with Realtek AC'97 CODECs.