Toslink is not the same as AT&T (aka "ST") optical. Theta makes something called the "Lineque" converter that sometimes has an "ST" connector -sometimes not. See the following...
https://www.audiogon.com/listings/lis974e9-theta-timebase-linque-conditioner-signal-processor-13876-...
https://www.audiogon.com/listings/lis974e9-theta-timebase-linque-conditioner-signal-processor-13876-...