I had a similar problem
The quality improved by adding a very decent USB cable (FTA sinope), Innuos Phoenix USB and power filtering, but was still too digital. Too hard.
What fixed it was the ethernet stage, namely adding an Uptone EtherRegen, then further expansion of its secondary components: LPS, fiber input into its SFP slot, and finally a clock. It now sounds smooth, rich, detailed and very musical. What sibilance previously existed has now gone.
Given I'm reclocking the Zenith's output already, it's remarkable how also reclocking the ethernet stage improves things further.
With the new EtherRegen out in June you should see plenty of v1 on eBay etc