imac thunderbolt port not recognising hardware

I recently purchased a late 2012 27' imac 3.4GHz, i7. The things works beautifully, however I'm having a particular issue with the thunderbolt ports. It's not recognising hardware I plug in - to either port. I've done a fair bit of research - done the whole restart thing, tried different combinations of connecting and booting up, uninstalling and re-installing the hardware drivers I'm trying to connect, used previous versions of the drivers, tested the hardware on my old macbook pro and it worked, but the new imac is just not recognising it through the thunderbolt ports. Specifically, the hardware is a Mbox 3 Pro, with Firewire 800 to 400 to thunderbolt cable. Long chain, but I do know it works. Any help/ideas on getting the imac and hardware to communicate would be greatly appreciated 🙂