I found a solution that might work install nanoserver on vmware then remote it with hyper manager connect the ramdisk directly to hyper -v not via nana server duno if its possible but i will try
if your question is how to run an x64 OS as a guest on VirtualBox or VMware IF you have Hyper-V installed ??? if the latter is the case you have to add an entry to your BCD with Hypervisor OFF. Windows will not allow any other VM software to run x64 guests while Hypervisor is on. use google and search "BCDedit Hypervisor"