That is very unfortunate indeed -- we've never run into that before, and don't have any other reports of that. There apparently were some issues with Unity 3D (the game engine that Tidalis runs on) doing that on some hardware
, but largely that was pre-2.6. Tidalis is currently running on 2.61 of Unity. In the next couple of weeks we'll be upgrading it to the newly-released Unity 3.0, which will have numerous benefits for Tidalis, but I don't know if the audio playback issue you're seeing will be one of them.
My main suggestion would of course be to check the sound drivers, which it sounds like you've already done; beyond that, about the only thing we can do is the upgrade to Unity 3.0, which is coming in the next few weeks, anyway. I really hate that, but that's one of the drawbacks of using someone else's engine (weighed against the many, many benefits). Sorry about that, hopefully that is of some help at least.