I guess to cut down on a bit of the latency but still allow for GPGPU acceleration, we need to convince AMD/nVidia to start shipping GPUs that have audio connectors on the back, just like they currently have video connectors?
On that note, HDMI actually is an audio connector.... I wonder how the transfer of audio to the GPU for HDMI currently works?
So I just figured out that my nVidia card actually has HDMI (and I was still using DVI because that's what I've always used...) and that there's this mysterious sound driver that you can optionally install with the display driver (which I never did of course, not seeing any reason for that).
Turns out if you plug in a HDMI cable and install that driver, it works just fine indeed. No extra cable, sound comes out of HDMI (actually, that's not very surprising, but... duh me). Don't ask me how it works, but it works really well.
There are no big DSP effects to tweak (or I haven't found them), just volume and balance, and you can select the sample rate (44.1kHz/48kHz). But... sound comes out when it's supposed to (no noticeable lag whatsoever), and quality is excellent.
So my guess would be that the driver probably just does the bare minimum as to qualify as "sound device" to Windows, and uploads the samples via PCIe, and then the display controller just mixes them into HDMI. Or something. From the available features, it doesn't look like there's some hefty GPGPU sound processing going on, anyway.