Digital Audio Output Differences? Is USB Audio Really The Top-notch?

As @david_ten  mentioned, having multiple port output options gives you versatility in choosing a DAC.

USB is used in some better DAC designs that run in asynchronous mode.  Among other advantages, these DACs apply their own internal clock, thus eliminating jitter. 

However, other port types besides USB  have more recently been configured to run in asynchronous mode, including S/PDIF and AES/EBU.

  Also other excellent DACs exist that use completely different approaches and are not reliant upon USB ports. PS Audio, for example, with I2S, etc.

Do you have a DAC?

Since most dacs optimized for usb these days, likely best output for streamer. However, one could have that rare dac in which usb not optimized in which case I2S could be preferred. The problem with I2S is no pin and/or connector standardization.

+1 to @sandstone 's post:

USB is used in some better DAC designs that run in asynchronous mode.  Among other advantages, these DACs apply their own internal clock, thus eliminating jitter. 

However, other port types besides USB  have more recently been configured to run in asynchronous mode, including S/PDIF and AES/EBU.

  Also other excellent DACs exist that use completely different approaches and are not reliant upon USB ports. PS Audio, for example, with I2S, etc.

What is your DAC? First things first, you can only use the outputs in your streamer that your DAC supports as inputs.

And as you already have bought the streamer, you can easily try all the outputs for yourself, with your DAC, in your home. Yes, you will have to spend some of your time with experimenting, and buy some cables, but it's part of the fun. There is really nothing to prevent you from trying for yourself.