(In reply to comment #5)
> The mainboard a MicroStar MS-7318. Based on the information on
> http://www.medion.com/de/service/_lightbox/treiber.php?msn=10010251 I think
> it is a VIA Hyperion Pro.

I strongly suspect the VIA chipset has broken MSI support and probably needs a
quirk to disable it.  I don't see any MSIs getting triggered:

  64:          0          0   PCI-MSI-edge      aerdrv, PCIe PME, pciehp
  65:          0          0   PCI-MSI-edge      aerdrv, PCIe PME, pciehp
  66:          0          0   PCI-MSI-edge      aerdrv, PCIe PME
  67:          0          0   PCI-MSI-edge      aerdrv, PCIe PME
  68:          0          0   PCI-MSI-edge      snd_hda_intel
  69:          0          0   PCI-MSI-edge      snd_hda_intel

Does sound work ok?