[ubuntu] Moving from vmware to something else?

I currently have a custom NAS box which is running Ubuntu 16.04.1 LTS and its the only linux machine i've ever had so my knowledge in this area is limited so i'm turning to the forums for some advice and guidance.

As well as being a big set of disks on the network, this NAS box also has 96GB of RAM so im using it to provide a virtual server currently running VMware workstation 11. I would like to be able to run newer Windows Server 2016 VMs in the future which apparently Workstation 11 doesnt support. I have two options which are pay another £115 for yet another upgrade or move away from VMware Workstation 11 to something else. The key requirement is to do this without having to destroy and rebuild the NAS box in the process.

I have so far looked at Xen, KVM, Proxmox VE. I think Proxmox VE is out because their website says the bare-metal installer wipes all existing data. So that sort of leaves Xen, KVM and whatever else might be suggested.

I'm not especially bothered about the solution being open source although I would be happy if it was. I just object to having to shell out cash to VMware every time Microsoft release a new operating system.

Thanks
Ian