Forget the internal DAC in the Innuos — your Bifrost DAC is better. Looks like Schiit uses a proprietary USB input so I’d tend to go with that out of your Innuos. Here’s a very good USB cable that won’t break the bank but physically separates the data and power legs of the cable that you don’t tend to find until spending much more $$$.
https://www.lavricables.com/cables/ultimate-silver-dual-usb-a-b-interconnect-cable/
After that, your most cost-effective upgrade may be a used Innuos linear power supply for your Zen Mini you can get for $400-$500 — it takes your streamer to a much higher level of performance. Hope this helps, and best of luck.