Thanks for the news Vincent. On your last post, Windows 8 will definitely run on ARM.
What is being offloaded is standard windows pipeline for audio which includes volume control for each application, mixing of the sound between apps, and other processing like low-pass filtering for subs and such. New driver model allows hardware to say that it can perform the same functions so the OS simply passes the application audio streams to it to perform them. As Vincent says, whether this results in better or worse fidelity is unknown. The OS currently uses floating point math to perform these functions so even though people scuff at any processing of audio samples in the OS, it does the job as well as it can.
In our scenarios here of playing 2-channel audio exclusively on a PC, there is no measurable CPU overhead in doing any of this since there is no mixing going on and just a volume control. Off-loading then provides no value, putting aside the fact that many people bypass the whole Windows pipeline anyway.
I suspect what is being done is to end a war that started with Vista. No sooner than this new kernel pipeline was put in that everyone went around it and made all of the new functionality useless. Hardware companies were marketing the above processing as features and didn't like to be commoditized this way. The new model allows them to reclaim these features as marketing bullet points.