Make sure you've already installed Whonix-Gateway (either the POWER or x86 version should work fine) prior to installing Whonix-Workstation.
Verify and Decompress the download as per the Whonix instructions.
Download the File:Whonix-Workstation-XFCE-qemu.patch to the same folder where you decompressed Whonix.
Run the following commands:
mv Whonix-Workstation*.xml Whonix-Workstation-XFCE.xml patch -i Whonix-Workstation-XFCE-qemu.patch
Import the VM and move the image file as per the Whonix instructions.
You're done, the Whonix-Workstation VM should now be usable. You may wish to add a tablet device in virt-manager for better mouse UX.