> CPUs just got fast enough that all of that, including 3d calcs, could be done better on common CPU by the mid-2000s. Do it on a sound card, you have to buy a new sound card to get improvements. Do it directly in the OS or in-game, and you can benefit from improvements from the OS or library or game devs immediately.

A dedicated chip is often better than a general purpose CPU (hello GPUs?). Game audio made a huge step back with Vista and beyond. Since audio cards could no longer do what they used to because of the limited driver model and developers/studios were more focused on graphical fidelity and physics calculations, nobody was going to waste precious CPU cycles on audio, at least not any more than the bare minimum.