Mac Tunderbolt Cable to Optical Cable

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As Doggiehowser suggests your best bet to the most direct route to your Benchmark may be a USB to SPDIF converter. A relatively inexpensive and good quality device is the Music Fidelity V-Link. You'd probably have to find a used one but there's one on ebay now for $79.

There are other similar devices but that's one I've used and it worked very well.

At the moment, there aren't any Thunderbolt audio devices I am aware of.

You can however get FireWire to coax/AES - Weiss INT202/203

Or you can get USB2.0 to coax/AES/optical/BNC. I use a Wavelink HS which provides a BNC SPDIF output. You can also try Bel Canto REF Link which outputs AES and coax and optical, Berkeley Alpha USB, among others.

If you don't have a spare USB or FW port - like with a MacBook Air/Retina, you can buy Thunderbolt to Firewire adaptors from Apple, or a Belkin Thunderbolt dock that provides Firewire/USB3.0 ports

http://www.belkin.com/us/F4U055-Belkin/p/P-F4U055/