PCI Passthrough Issue

Hi there!

I am trying to pass a PCI Graphics Card (HIS Radeon R7 260x) to a Win7 VM.

I did the steps I could find on the internet / in this forum:

- Identifying the device with lspci -n

- freeing the card from any drivers (two devices, one is gfx, the other snd hdmi device)

echo "1002 6658" > /sys/bus/pci/drivers/pci-stub/new_id
echo "0000:01:00.0" > /sys/bus/pci/drivers/ahci/unbind
echo "0000:01:00.0" > /sys/bus/pci/drivers/pci-stub/bind
echo "1002 6658" > /sys/bus/pci/drivers/pci-stub/remove_id

echo "1002 aac0" > /sys/bus/pci/drivers/pci-stub/new_id
echo "0000:01:00.1" > /sys/bus/pci/drivers/ahci/unbind
echo "0000:01:00.1" > /sys/bus/pci/drivers/pci-stub/bind
echo "1002 aac0" > /sys/bus/pci/drivers/pci-stub/remove_id

- Finally adding the devices to the vm via qm monitor:
# device_add pci-assign,host=01:00.0,id=gfx

Host-side INTx sharing not supported, using MSI instead
Some devices do not work properly in this mode.

# device_add pci-assign,host=01:00.1,id=snd

The soundcard seems worked fine (windows driver gets loaded),
but the graphiccard does not load the driver.
There is this yellow exclamation mark sign in the windows device manager.

I assume that this is related to the warning, that Host-side INTx sharing is not supported.
Is there a way to simply switch that on? I read in the forum, that it was turned on by default in some older versions, but caused trouble.

Any suggestions and help is much appreciated!
Nils