@SqueamishNerd I don't think it's possible to go above 255. That's definitely the limit, and it's also 16 squared minus one, which makes me think the value might actually be two hexidecimal digits long. In that case, there would only be 256 distinct values, 0-255, and trying to change the number would either accomplish nothing or break something. You can of course try if you want; at worst, you'll just need to delete Options.ini again.
Your dxdiag shows that the Realtek sound driver is quite old, perhaps as old as the system itself. Please check for an updated driver on the download page for your motherboard. I can't tell which model you have from your dxdiag, but if you list the motherboard model, I'll take a look. Or you may be able to find it yourself—the Asus product pages are reasonably easy to use.
If Asus doesn't offer a newer driver, try asking Windows to look for one. Hit Windows key-X, choose the Device Manager, open the Audio section, right-click on the Realtek entry, and click the black and green Update menu button. There may be multiple Realtek entries; be sure to get them all. While you're there, you might as well have Windows look for new drivers for any other audio devices as well as everything in the Sound section. Restart your computer when you're done and before trying to play.
If that doesn't help, please post a new dxdiag so I can see the new driver versions, if any.
