Direct audio to the Fireface UCX? Sure, you can do that, but you won't need all those Tethers and Links since the UCX has no D-Sub audio I/O. But since the UCX also has lightpipe I/O, you could later attach an ADAT lightpipe interface that has the DC-coupled I/O that Silent Way/CV Tools/Volta/etc wants to use, and go back to that idea when it's a better fit. In that case, my suggestion would be the ES-8, with four inputs and eight outputs. But right now, you can just tie your audio outs directly into the Fireface UCX although I STRONGLY suggest you have an attenuatable stereo output module so that you can avoid clips due to the level mismatch between synth and pro audio levels. Something like, say, the Happy Nerding Isolator, which has the ganged stereo control and also has transformer isolation to help deal with hum and noise.