Hi
Usually, front ports are connected to one controller, and back ports to another. However, this may be different in your PC.
If you say that the front ports are busted, then it's possible you're left with only 1 USB 2.0 controller working.
And USB 3.0 controller may have compatibility issues with PS Eye. See known compatibility problems in the bottom of this article:
http://wiki.ipisoft.com/USB_controllersTo find out which port is connected to which controller, switch Device Manager to "Devices by Connection" view. Take a single camera and connect it sequentially to all USB ports. Each time, watch in Device Manager under which USB controller node appears the camera node.
If you confirm that there is only 1 USB controller suitable for connection PS Eye cameras, then you'll need an extension card. Usually, PCI cards are USB 2.0, and PCIe cards are USB 3.0. You can choose what best suits you. Just be aware of compatibility issues - use the mentioned above compatibility table to avoid buying incompatible USB controller.