GPU Passthrough - IOMMU not working for me - on SkyLake 16.04 AsRock

I read this thread on GPU Passthrough working on Ubuntu 16.04:
http://ubuntuforums.org/showthread.php?t=2320369

And I read the most relevant articles,
including those from
vfio.blogspot.co.uk and
www.pugetsystems.com/labs/articles/Multiheaded-NVIDIA-Gaming-using-Ubuntu-14-04-KVM-585/

*** OS:

(K)Ubuntu 16.04.0 booting from UEFI

***HARDWARE:

i7 6700-k (which supports VT-D)
motherboard AsRock ( Fatal1ty Z170 Gaming ITX ac ) which has got both VT-D and Intel Virtualization "enabled".
GTX 970 destined to GPU passthrough with qemu and KVM
intel integrated graphics destinate to the host. (bios primary display setting = "integrated" )

***PROBLEM:
dmesg | grep -e DMAR -e IOMMU

results in:

[ 0.000000] DMAR: IOMMU enabled

however typing:

find /sys/keel/iommu_groups/ -type l

results in:
no output at all

*** SETTINGS:

I tried with all of these:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi=off intel_iommu=on "
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi=off intel_iommu=on intel_iommu=igfx_off"
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi=off intel_iommu=on intel_iommu=igfx_off pcie_acs_override=downstream"

always followed by sudo update-grub and reboot, of course.

I need acpi=off in my system, otherwise dmesg shows a ton of waings that keep growing.
Those waing are not likely to be related to the problem with IOMMU

I also have got the following settings:

sudo kate /etc/modules

pci_stub
vfio
vfio_iommu_type1
vfio_pci
kvm
kvm_intel