Sure, However I did the bare amount of changes to make it work, keep in mind that this will change the behaviour of all qubes using qemu-stubdom-linux-full-rootfs, not only Windows, you’ll only be able to use sys-audio as the audiovm for those qubes.
If despite all the flaws anyone wants to try this: (Remember to keep a copy of qemu-stubdom-linux-full-rootfs in case you want to easily revert the changes)
mkdir /tmp/stubdom-full
cd /tmp/stubdom-full
cp /usr/libexec/xen/boot/qemu-stubdom-linux-full-rootfs qemu-stubdom-linux-full-rootfs.gz
gunzip qemu-stubdom-linux-full-rootfs.gz
cpio -i -d -H newc --no-absolute-filenames < qemu-stubdom-linux-full-rootfs
rm qemu-stubdom-linux-full-rootfs
vim init (Using your text editor of choice find module-vchank-sink and change the value of domid from 0 to the xid of sys-audio, you can find the xid using qvm-prefs sys-audio | grep -w xid, after that save and exit)
find . -print0 | cpio --null -ov --format=newc | gzip -9 > ../qemu-stubdom-linux-full-rootfs
cp ../qemu-stubdom-linux-full-rootfs /usr/libexec/xen/boot/qemu-stubdom-linux-full-rootfs
Now you should be able to have sound using sys-audio as your audiovm for Windows, if not let me know.