[[ Will have to bite the bullet and buy a new interface. ]]
Does your iMac have firewire available?
The advantage of firewire over USB, insofar as audio interfaces are concerned, is that you don't need any "drivers" at all. So long as the firewire-based interface is "CORE Audio compliant" (all modern ones seem to be), they will utilize the built-in drivers that are part of the Mac OS. Just plug in the interface, and the OS "sees it" immediately, and makes it available to your DAW apps. No "driver conflicts", now or in the future.
I understand that the latest versions of the Mac OS now have some kind of CORE Audio drivers for USB, as well. But it may take USB-based interfaces a while to catch up, as this is a hardware/firmware requirement with the USB "box" itself.
If your Mac is one of the newest and has only thunderbolt (no firewire ports), you can buy the $30 thunderbolt-to-firewire adapter, and use that with a firewire interface.
Steinberg offers some USB-based interfaces that look to be decent -- and they provide an "integrated solution" with Steinberg's Cubase software as well. I've been a Cubase fan for years.
I don't use Steinberg hardware, though. I've got an Echo "Audiofire8" that has been flawless in its operation.
If you're hunting for another interface, and are willing to consider firewire, you might try hunting up a used Audiofire4 or even the Audiofire8. They are no longer sold new, but can be found used (ebay, etc.) at decent prices. Nice equipment!