The Tobii REX doesn’t require USB 3.0, but it does require a USB driver of its own which is not included in the EyeX installation. (The EyeX installation includes drivers for the EyeX Controller eye tracker device only).
The required Tobii USB Service for Windows can be found on the Downloads page (click the plus-sign in the “Other Tobii Tech devices” section to expand the list). When the driver is successfully installed it will also come up on the About page in EyeX Settings.
I also suggest you upgrade to the latest firmware – a number of improvements have been made since the 0.9.3 firmware. The latest Tobii REX firmware package is found in the same place as the USB service, and you can use the firmware upgrade feature on the About page in EyeX Settings to do the upgrade (button only visible when the REX is connected to the computer).