xerox printers on virtual servers

Hi

we have currently converted all our server on to a citrix XenSan and 2 out of the 10 xerox printers we have..both fx docucentre-II c7500 are extremely slow to print even a 5kb document (1.5hrs to be exact). Now i have another xerox unit exact specs as the other 2 that dont print and it prints fine. i have logged support call with xerox and they say its the xenserver causing the issues. If thats the cause why dont i have the issue with the other 20 printer i have on the virtual machine?

any ideas would be really helpfull