Consegui encontrar a resposta para qualquer pessoa que tenha o mesmo problema. Este post sobre unraid explica tudo, atualizou meu kernel da versão padrão que vem com o ubuntu 16.04 e o problema foi resolvido.
Estou executando uma máquina virtual do Windows 10 como meu driver diário, ele está sendo executado em cima do servidor ubuntu 16.04. A passagem de placa de expansão GPU e USB funciona muito bem, mas estou com CPU host maximizada (aparece como "sistema" de uso da CPU, mas está no qemu htop) quando o convidado toca QUALQUER áudio, independentemente do hipervisor fornecido ich9 placa de som, placa de som on-board transmitida (ela está em seu próprio grupo IOMMU!) ou a placa de som integrada na GPU.
A placa de som onboard passada é incorporada no chipset Z97.
Aqui está o arquivo xml da VM:
<domain type='kvm' id='1' xmlns:qemu='http://libvirt.org/schemas/domain/qemu/1.0'>
<name>Windowz</name>
<uuid>d7c7a1da-2083-49a0-a968-6f28ca9c914e</uuid>
<memory unit='KiB'>20971520</memory>
<currentMemory unit='KiB'>20971520</currentMemory>
<vcpu placement='static'>4</vcpu>
<resource>
<partition>/machine</partition>
</resource>
<os>
<type arch='x86_64' machine='pc-i440fx-xenial'>hvm</type>
</os>
<features>
<acpi/>
<apic/>
<hyperv>
<relaxed state='on'/>
<vapic state='on'/>
<spinlocks state='on' retries='8191'/>
</hyperv>
</features>
<cpu mode='host-passthrough'>
<topology sockets='1' cores='4' threads='1'/>
</cpu>
<clock offset='localtime'>
<timer name='rtc' tickpolicy='catchup'/>
<timer name='pit' tickpolicy='delay'/>
<timer name='hpet' present='no'/>
<timer name='hypervclock' present='yes'/>
</clock>
<on_poweroff>destroy</on_poweroff>
<on_reboot>restart</on_reboot>
<on_crash>restart</on_crash>
<pm>
<suspend-to-mem enabled='no'/>
<suspend-to-disk enabled='no'/>
</pm>
<devices>
<emulator>/usr/bin/qemu-system-x86_64</emulator>
<disk type='file' device='cdrom'>
<driver name='qemu' type='raw'/>
<backingStore/>
<target dev='sda' bus='sata'/>
<readonly/>
<boot order='2'/>
<alias name='sata0-0-0'/>
<address type='drive' controller='0' bus='0' target='0' unit='0'/>
</disk>
<disk type='file' device='cdrom'>
<driver name='qemu' type='raw'/>
<backingStore/>
<target dev='sdb' bus='sata'/>
<readonly/>
<alias name='sata0-0-1'/>
<address type='drive' controller='0' bus='0' target='0' unit='1'/>
</disk>
<disk type='block' device='disk'>
<driver name='qemu' type='raw' cache='none' io='native'/>
<source dev='/dev/sdd'/>
<backingStore/>
<target dev='vdc' bus='virtio'/>
<alias name='virtio-disk2'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x0e' function='0x0'/>
</disk>
<disk type='block' device='disk'>
<driver name='qemu' type='raw' cache='none' io='native'/>
<source dev='/dev/nvme0n1'/>
<backingStore/>
<target dev='vdd' bus='virtio'/>
<boot order='1'/>
<alias name='virtio-disk3'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x0f' function='0x0'/>
</disk>
<disk type='block' device='disk'>
<driver name='qemu' type='raw' cache='none' io='native'/>
<source dev='/dev/sdb'/>
<backingStore/>
<target dev='vde' bus='virtio'/>
<alias name='virtio-disk4'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x08' function='0x0'/>
</disk>
<disk type='block' device='disk'>
<driver name='qemu' type='raw' cache='none' io='native'/>
<source dev='/dev/sdc'/>
<backingStore/>
<target dev='vdf' bus='virtio'/>
<alias name='virtio-disk5'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x09' function='0x0'/>
</disk>
<controller type='pci' index='0' model='pci-root'>
<alias name='pci.0'/>
</controller>
<controller type='sata' index='0'>
<alias name='sata0'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/>
</controller>
<controller type='virtio-serial' index='0'>
<alias name='virtio-serial0'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/>
</controller>
<controller type='usb' index='0' model='nec-xhci'>
<alias name='usb'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/>
</controller>
<interface type='user'>
<mac address='52:54:00:5d:ea:ef'/>
<model type='virtio'/>
<alias name='net0'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
</interface>
<channel type='spicevmc'>
<target type='virtio' name='com.redhat.spice.0' state='disconnected'/>
<alias name='channel0'/>
<address type='virtio-serial' controller='0' bus='0' port='1'/>
</channel>
<input type='mouse' bus='ps2'/>
<input type='keyboard' bus='ps2'/>
<graphics type='vnc' port='5900' autoport='no' listen='0.0.0.0'>
<listen type='address' address='0.0.0.0'/>
</graphics>
<sound model='ich9'>
<alias name='sound0'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
</sound>
<video>
<model type='qxl' ram='65536' vram='65536' vgamem='16384' heads='1' primary='yes'/>
<alias name='video0'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
</video>
<hostdev mode='subsystem' type='pci' managed='yes'>
<driver name='vfio'/>
<source>
<address domain='0x0000' bus='0x06' slot='0x00' function='0x0'/>
</source>
<alias name='hostdev0'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x0a' function='0x0'/>
</hostdev>
<hostdev mode='subsystem' type='pci' managed='yes'>
<driver name='vfio'/>
<source>
<address domain='0x0000' bus='0x06' slot='0x00' function='0x1'/>
</source>
<alias name='hostdev1'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x0b' function='0x0'/>
</hostdev>
<hostdev mode='subsystem' type='pci' managed='yes'>
<driver name='vfio'/>
<source>
<address domain='0x0000' bus='0x07' slot='0x00' function='0x0'/>
</source>
<alias name='hostdev2'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x0d' function='0x0'/>
</hostdev>
<hostdev mode='subsystem' type='pci' managed='yes'>
<driver name='vfio'/>
<source>
<address domain='0x0000' bus='0x00' slot='0x1b' function='0x0'/>
</source>
<alias name='hostdev3'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x10' function='0x0'/>
</hostdev>
<redirdev bus='usb' type='spicevmc'>
<alias name='redir0'/>
<address type='usb' bus='0' port='1'/>
</redirdev>
<redirdev bus='usb' type='spicevmc'>
<alias name='redir1'/>
<address type='usb' bus='0' port='2'/>
</redirdev>
<memballoon model='virtio'>
<alias name='balloon0'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x0c' function='0x0'/>
</memballoon>
</devices>
<qemu:commandline>
<qemu:arg value='-redir'/>
<qemu:arg value='tcp:1339::1337'/>
<qemu:arg value='-redir'/>
<qemu:arg value='tcp:3819::3819'/>
<qemu:arg value='-redir'/>
<qemu:arg value='tcp:29176::29176'/>
</qemu:commandline>
</domain>
Consegui encontrar a resposta para qualquer pessoa que tenha o mesmo problema. Este post sobre unraid explica tudo, atualizou meu kernel da versão padrão que vem com o ubuntu 16.04 e o problema foi resolvido.