Hyper-V cannot be installed: The processor does not have the required virtualization capabilities.

I am trying to use Visual Studio 2013 with Windows Phone SDK 8.0 on Windows 8.1 Enterprise running as a guest in a VirtualBox virtual machine hosted from Windows 7 Ultimate.  The Windows Phone emulator in Visual Studio will not work.  The guest Hardware Virtualization settings for VT-x and Nested Paging are selected.  The BIOS setting for Virtualization is enabled.  However, in the guest Windows 8.1 features settings, the "Hyper-V Platform" option is disabled and indicates that the "Hyper-V cannot be installed:  The processor does not have the required virtualization capabilities."  However, I checked on my processor which is an Intel (Clarksfield), I7-740QM 1.73 and it supports Hyper-V, SLAT/EPT.  My BIOS has only a single option for enabling Virtualization but none of the other SLAT/EPT, VMX, XD options.  I am lost here.  Is there a solution?  Do I need to use Visual Studio 2013 and Windows Phone SDK 8.0 directly on a Windows 8.1 host and not through a virtual machine?