QEMU support has been deprecated in favor of KVM. The slow performance of pure emulation makes it impractical for the majority of Linux users. Most consumer systems should support the hardware virtualization extensions required by KVM. 
- This wiki entry formerly stated:
You can run Whonix ™ with QEMU instead of VirtualBox or KVM as well. There is no specific documentation about QEMU, because instructions would be very similar to the instructions on Whonix ™ KVM wiki page. Instead of importing Whonix ™ KVM Templates, you can simply import Whonix ™ QEMU Templates.