How to interface multiple USB UIRT devices

How to interface multiple USB UIRT devices from one machine using C++. In the API list I do not see any API to distinguish between different USB hardware, though I came across an API in this post http://www.usbuirt.com/phpBB2/viewtopic.php?t=895. The API is UUIRTOpenEx("USB-UIRT", 0, NULL, NULL).
My requirement is to simultaneously drive multiple USB UIRT hardware each on its own thread if possible, to control multiple STBs.
My requirement is to simultaneously drive multiple USB UIRT hardware each on its own thread if possible, to control multiple STBs.