Initially I got the same result as you, with a working sierra 10.12.5 VM.
I then started to work thru the problem with a new el capitan VM (10.11.6). Using the most recent Clover (r4097).
With the following vm xml and clover config.plist, it works well. I can also passthrough AMD graphics card and USB 3 PCI card.
Still haven't been successful with a new Sierra VM. It got stuck while booting the installer. This seems to be a reported problem since 10.12.4. Would like to try again with a patched qemu 2.9.0 (applesmc patched).
<domain type='kvm' id='64' xmlns:qemu='http://libvirt.org/schemas/domain/qemu/1.0'>
<name>qemu el capitan- ovmf - try</name>
<uuid>0450821b-8594-5d90-dd1b-c84fe897c924</uuid>
<metadata>
<vmtemplate xmlns="unraid" name="Linux" icon="linux.png" os="linux"/>
</metadata>
<memory unit='KiB'>4194304</memory>
<currentMemory unit='KiB'>4194304</currentMemory>
<memoryBacking>
<nosharepages/>
</memoryBacking>
<vcpu placement='static'>2</vcpu>
<cputune>
<vcpupin vcpu='0' cpuset='7'/>
<vcpupin vcpu='1' cpuset='6'/>
</cputune>
<resource>
<partition>/machine</partition>
</resource>
<os>
<type arch='x86_64' machine='pc-q35-2.9'>hvm</type>
<loader readonly='yes' type='pflash'>/usr/share/qemu/ovmf-x64/OVMF_CODE-pure-efi.fd</loader>
<nvram>/etc/libvirt/qemu/nvram/0450821b-8594-5d90-dd1b-c84fe897c924_VARS-pure-efi.fd</nvram>
<boot dev='hd'/>
</os>
<features>
<acpi/>
<apic/>
</features>
<cpu mode='host-passthrough' check='none'>
<topology sockets='1' cores='2' threads='1'/>
</cpu>
<clock offset='utc'/>
<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'/>
<source file='/mnt/cache/vm_images/clover-qemu29.img'/>
<backingStore/>
<target dev='hda' bus='sata'/>
<alias name='sata0-0-0'/>
<address type='drive' controller='0' bus='0' target='0' unit='0'/>
</disk>
<disk type='file' device='disk'>
<driver name='qemu' type='raw'/>
<source file='/mnt/cache/vm_images/ElCapitan.img'/>
<backingStore/>
<target dev='hdb' bus='sata'/>
<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='dmi-to-pci-bridge'>
<model name='i82801b11-bridge'/>
<alias name='pci.1'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x1e' function='0x0'/>
</controller>
<controller type='pci' index='2' model='pci-bridge'>
<model name='pci-bridge'/>
<target chassisNr='2'/>
<alias name='pci.2'/>
<address type='pci' domain='0x0000' bus='0x01' slot='0x01' function='0x0'/>
</controller>
<interface type='bridge'>
<mac address='52:54:00:00:20:30'/>
<source bridge='br0'/>
<target dev='vnet2'/>
<model type='e1000-82545em'/>
<alias name='net0'/>
<address type='pci' domain='0x0000' bus='0x02' slot='0x03' function='0x0'/>
</interface>
<serial type='pty'>
<source path='/dev/pts/2'/>
<target port='0'/>
<alias name='serial0'/>
</serial>
<console type='pty' tty='/dev/pts/2'>
<source path='/dev/pts/2'/>
<target type='serial' port='0'/>
<alias name='serial0'/>
</console>
<input type='mouse' bus='ps2'>
<alias name='input0'/>
</input>
<input type='keyboard' bus='ps2'>
<alias name='input1'/>
</input>
<graphics type='vnc' port='5901' autoport='yes' websocket='5701' listen='0.0.0.0' keymap='en-us'>
<listen type='address' address='0.0.0.0'/>
</graphics>
<video>
<model type='cirrus' vram='16384' heads='1' primary='yes'/>
<alias name='video0'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x0'/>
</video>
<memballoon model='none'>
<alias name='balloon0'/>
</memballoon>
</devices>
<seclabel type='none' model='none'/>
<qemu:commandline>
<qemu:arg value='-device'/>
<qemu:arg value='usb-kbd'/>
<qemu:arg value='-device'/>
<qemu:arg value='usb-tablet'/>
<qemu:arg value='-device'/>
<qemu:arg value='Xxxxxxxxxxxxxxxxxxxxxxxxx'/>
<qemu:arg value='-smbios'/>
<qemu:arg value='type=2'/>
<qemu:arg value='-cpu'/>
<qemu:arg value='IvyBridge,vendor=GenuineIntel,kvm=on,+invtsc,vmware-cpuid-freq=on'/>
</qemu:commandline>
</domain>
Config.plist
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>Boot</key>
<dict>
<key>Arguments</key>
<string>-v</string>
</dict>
<key>RtVariables</key>
<dict>
<key>BooterConfig</key>
<string>0x28</string>
<key>CsrActiveConfig</key>
<string>0x67</string>
<key>ROM</key>
<string>UseMacAddr0</string>
</dict>
<key>SMBIOS</key>
<dict>
<key>BiosReleaseDate</key>
<string>09/03/2013</string>
<key>BiosVendor</key>
<string>Apple Inc.</string>
<key>BiosVersion</key>
<string>IM142.88Z.0118.B00.1309031249</string>
<key>Board-ID</key>
<string>Xxxxxxxxxxxxxxxxxx</string>
<key>BoardManufacturer</key>
<string>Apple Inc.</string>
<key>BoardType</key>
<integer>10</integer>
<key>ChassisAssetTag</key>
<string>iMac-Aluminum</string>
<key>ChassisManufacturer</key>
<string>Apple Inc.</string>
<key>ChassisType</key>
<string>13</string>
<key>Family</key>
<string>iMac</string>
<key>Manufacturer</key>
<string>Apple Inc.</string>
<key>ProductName</key>
<string>iMac14,2</string>
<key>SerialNumber</key>
<string>Xxxxxxxxxxxxxxxxxx</string>
<key>Trust</key>
<false/>
<key>Version</key>
<string>1.0</string>
</dict>
</dict>
</plist>