From USB to AES/EBU ,it needs much much more than simply a connector!!!
Hence,impossible to find one,especially with acceptable quality for audio!
That is a great system placed in a very nice room. You must try an Empirical Audio Off-Ramp Turbo ( usb to aes-ebu). I am burning one in right now and I feel like it is the missing link to extract the most from computer audio.
I have been using a computer for my transport for over 3 years now and could NEVER go back to playing silver discs. Plus I am burning vinyl onto my hardrive at 24/96 and the sound is really nice. Have fun.