Coaxial - USB from DAC

Why do you need to use a coax splitter for your DAC? I am having a hard time finding the cause for this in the original post (sorry if my comprehension is failing us).

The USB output from PCs are generally poor to begin with. The long USB cable run isn't necessarily helping. My best suggestion in your usage case would be to feed a DDC from your PC via USB, and let the DDC regenerate/reclock the signal before outputting it to your DAC. The DDC will also have multiple output formats for you to experiment with, as I see your DAC offers a couple of different input formats (at least USB and coax S/PDIF, if not more). A DDC would let you test which format works best (this varies by DAC).

You're not running a very expensive DAC, so a very expensive DDC makes little sense. Perhaps consider trying a Douk U2 Pro or an SMSL PO100 Pro.

I run a Gustard U18 DDC which feeds my DAC via I2S.

-Ed

Got it, thanks- 

You’re running 30 feet of USB? Is it an active signal cable? USB 2.0 has a limited usable length of just over 13 feet (4 meters) so I would think your data rates are low. Either way I would look for a better solution.

Can you not use an optical cable from your Zen stream to your dac and then use the coaxial input to replace the USB from the computer?

There are AES/SPDIF splitters available but they are typically for distribution rather than acting as an A/B merging two devices into one input. 

Not an answer to your question, but a dedicated streamer placed with the rest of your components will likely sound a lot better and solve the problem. You can feed it with a wifi extender and short Ethernet cable to avoid a new problem). My high end systems runs on a wifi extenders. 

You cannot split SPDIF. And that is totally different than USB.