Just use a HDMI → HDMI+Audio adapter.
Many on Amazon for under $50. Like;
The connectivity would be;
- From your Nintendo Switch Hub HDMI Out to this Adapter’s HDMI IN.
- This Adapter’s HDMI OUT goes to your TV HDMI input
- This Adapter’s S/PDIF TOSLink OUT (or RCA) goes an appropriate Vivaldi S/PDIF input
- Set Vivaldi DAC clocking to “Audio” on that S/PDIF input port