Which virtual machine to choose for a terminal server?

Question

Virtualization

I want to assemble a server on an AMD EPIC processor, mother micro, put ubuntu and a virtual machine on it, the virtual machines will have: a terminal server, several web servers, a mail server, an asterisk.
Problem: Terminal Server needs a GPU (forward graphics card) as users open 10 folds of chrome and cycle through them.
The staff sysadmin wants to install Xen because he thinks it is the most convenient virtual machine, BUT the free version of Xen only supports 32 threads of the processor, and I want a processor with 64 threads.
In addition, I don’t know how Xen will behave when forwarding a video card.
There is still a need to balance the load on the cores, let's say one web server takes 8 threads during rush hour, and at night when other machines consume little, it could take more resources, since heavy database reindexing processes are launched at night.
Otherwise, of course, the free version of Xen suits us.
Tell me, maybe something is better tailored to our needs?