YOu can get a toslink to coax converter like Dms1 mentioned, but I don't see how it could make a difference. In fact, the extra conversion could make things worse.
Get a good glass mini toslink to toslink cable and call it a day. Or, a usb to spdif converter will also work if you are set on coax. ]
With a good dac, the glass toslink can sound excellent. I have determined that I prefer the glass toslink out of a mac mini to a certain asynchronous usb/coax converter that I own. The toslink sounds more relaxed and musical in my system. However, the difference between the two is not night and day.