[all variants] CUPS does not find all network printers with virtualbox

Hi all,

I'm not an expert of virtualbox and I'm doing some experiments to configure a small Xubuntu VM. Everything seems to work fine, including networking (I'm using the VM right now). However, when I try to add a network printer using CUPS, I can see only a subset of the printers I can see from my Linux host. I cannot understand why. Do you have any suggestion? :confused:

Thank you!

PS:
Of course, the printer I NEED to add, is not on the list of the printers I can see...