Lubo

No, not using IPVLAN.
Although the suggestion is appreciated, thanks @hawgorn

Actually just came back to this thread today to inform anyone from the future that I did manage to resolve this for me.
Essentially the solution for me was that I moved house and got a new ISP. New connection, new IP.
Not sure what change actually fixed it but I had wireguard up and running in 5 minutes :).

I suspect that my previous ISP was blocking it in someway? 
Anyways, that may be your issue too.
 

For those who suffer with the same issue as I was having I was able to solve the issue in the end.
For me, it was a combination of the following get rid of the Code 43:
Making sure the passthrough information had the correct function/slot/bus/multifunction. Adding "hidden state" to the kvm. See code. Adding a arbitraty value "123456789" to a vendor id. This solved the Code 43 and I was able to get sound from the card, however it had some serious issues. It slowed playback considerably, and sounded truly demonic haha.
In the end I was playing with different emulation machines, i440fx and Q53, and after I had eventually I found one which worked.

Occasionally I do have the demonic sound return however this can be solved simply with a system restart and it's so intermittent I am content with it for now.

Good luck! I am by no means an expert but I hope my experiences may prove helpful to others.
 

 
<?xml version='1.0' encoding='UTF-8'?> <domain type='kvm' id='2'> <name>Home Theatre VM</name> <uuid>282a2b72-4603-712c-a49b-e1ccf19fa21d</uuid> <metadata> <vmtemplate xmlns="unraid" name="Windows 10" icon="windows.png" os="windows10"/> </metadata> <memory unit='KiB'>2097152</memory> <currentMemory unit='KiB'>2097152</currentMemory> <memoryBacking> <nosharepages/> </memoryBacking> <vcpu placement='static'>4</vcpu> <cputune> <vcpupin vcpu='0' cpuset='0'/> <vcpupin vcpu='1' cpuset='1'/> <vcpupin vcpu='2' cpuset='2'/> <vcpupin vcpu='3' cpuset='3'/> </cputune> <resource> <partition>/machine</partition> </resource> <os> <type arch='x86_64' machine='pc-q35-7.1'>hvm</type> <loader readonly='yes' type='pflash'>/usr/share/qemu/ovmf-x64/OVMF_CODE-pure-efi.fd</loader> <nvram>/etc/libvirt/qemu/nvram/282a2b72-4603-712c-a49b-e1ccf19fa21d_VARS-pure-efi.fd</nvram> </os> <features> <acpi/> <apic/> <hyperv mode='custom'> <relaxed state='on'/> <vapic state='on'/> <spinlocks state='on' retries='8191'/> <vendor_id state='on' value='1234567890'/> </hyperv> <kvm> <hidden state='on'/> </kvm> </features> <cpu mode='host-passthrough' check='none' migratable='on'> <topology sockets='1' dies='1' cores='4' threads='1'/> <cache mode='passthrough'/> </cpu> <clock offset='localtime'> <timer name='hypervclock' present='yes'/> <timer name='hpet' present='no'/> </clock> <on_poweroff>destroy</on_poweroff> <on_reboot>restart</on_reboot> <on_crash>restart</on_crash> <devices> <emulator>/usr/local/sbin/qemu</emulator> <disk type='file' device='disk'> <driver name='qemu' type='raw' cache='writeback'/> <source file='/mnt/user/domains/Home Theatre Windows 10/vdisk1.img' index='2'/> <backingStore/> <target dev='hdc' bus='virtio'/> <boot order='1'/> <alias name='virtio-disk2'/> <address type='pci' domain='0x0000' bus='0x03' slot='0x00' function='0x0'/> </disk> <disk type='file' device='cdrom'> <driver name='qemu' type='raw'/> <source file='/mnt/user/isos/virtio-win-0.1.225-2.iso' index='1'/> <backingStore/> <target dev='hdb' bus='sata'/> <readonly/> <alias name='sata0-0-1'/> <address type='drive' controller='0' bus='0' target='0' unit='1'/> </disk> <controller type='usb' index='0' model='ich9-ehci1'> <alias name='usb'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x7'/> </controller> <controller type='usb' index='0' model='ich9-uhci1'> <alias name='usb'/> <master startport='0'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0' multifunction='on'/> </controller> <controller type='usb' index='0' model='ich9-uhci2'> <alias name='usb'/> <master startport='2'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x1'/> </controller> <controller type='usb' index='0' model='ich9-uhci3'> <alias name='usb'/> <master startport='4'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x2'/> </controller> <controller type='sata' index='0'> <alias name='ide'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x1f' function='0x2'/> </controller> <controller type='pci' index='0' model='pcie-root'> <alias name='pcie.0'/> </controller> <controller type='pci' index='1' model='pcie-root-port'> <model name='pcie-root-port'/> <target chassis='1' port='0x8'/> <alias name='pci.1'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x0' multifunction='on'/> </controller> <controller type='pci' index='2' model='pcie-root-port'> <model name='pcie-root-port'/> <target chassis='2' port='0x9'/> <alias name='pci.2'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x1'/> </controller> <controller type='pci' index='3' model='pcie-root-port'> <model name='pcie-root-port'/> <target chassis='3' port='0xa'/> <alias name='pci.3'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x2'/> </controller> <controller type='pci' index='4' model='pcie-root-port'> <model name='pcie-root-port'/> <target chassis='4' port='0xb'/> <alias name='pci.4'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x3'/> </controller> <controller type='pci' index='5' model='pcie-root-port'> <model name='pcie-root-port'/> <target chassis='5' port='0xc'/> <alias name='pci.5'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x4'/> </controller> <controller type='pci' index='6' model='pcie-root-port'> <model name='pcie-root-port'/> <target chassis='6' port='0xd'/> <alias name='pci.6'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x5'/> </controller> <controller type='virtio-serial' index='0'> <alias name='virtio-serial0'/> <address type='pci' domain='0x0000' bus='0x02' slot='0x00' function='0x0'/> </controller> <interface type='bridge'> <mac address='52:54:00:e0:c6:09'/> <source bridge='br0'/> <target dev='vnet1'/> <model type='virtio-net'/> <alias name='net0'/> <address type='pci' domain='0x0000' bus='0x01' slot='0x00' function='0x0'/> </interface> <serial type='pty'> <source path='/dev/pts/0'/> <target type='isa-serial' port='0'> <model name='isa-serial'/> </target> <alias name='serial0'/> </serial> <console type='pty' tty='/dev/pts/0'> <source path='/dev/pts/0'/> <target type='serial' port='0'/> <alias name='serial0'/> </console> <channel type='unix'> <source mode='bind' path='/var/lib/libvirt/qemu/channel/target/domain-2-Home Theatre VM/org.qemu.guest_agent.0'/> <target type='virtio' name='org.qemu.guest_agent.0' state='disconnected'/> <alias name='channel0'/> <address type='virtio-serial' controller='0' bus='0' port='1'/> </channel> <input type='mouse' bus='ps2'> <alias name='input0'/> </input> <input type='keyboard' bus='ps2'> <alias name='input1'/> </input> <audio id='1' type='none'/> <hostdev mode='subsystem' type='pci' managed='yes'> <driver name='vfio'/> <source> <address domain='0x0000' bus='0x01' slot='0x00' function='0x0'/> </source> <alias name='hostdev0'/> <rom file='/mnt/user/isos/GeforceGTX660.rom'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0' multifunction='on'/> </hostdev> <hostdev mode='subsystem' type='pci' managed='yes'> <driver name='vfio'/> <source> <address domain='0x0000' bus='0x01' slot='0x00' function='0x1'/> </source> <alias name='hostdev1'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x1'/> </hostdev> <hostdev mode='subsystem' type='usb' managed='no'> <source> <vendor id='0x046d'/> <product id='0xc52b'/> <address bus='1' device='2'/> </source> <alias name='hostdev2'/> <address type='usb' bus='0' port='1'/> </hostdev> <memballoon model='none'/> </devices> <seclabel type='dynamic' model='dac' relabel='yes'> <label>+0:+100</label> <imagelabel>+0:+100</imagelabel> </seclabel> </domain>