Best Digital Interface

Whether a USB or traditional digital output sounds better are completely dependent on the Streamer / DAC components you have. It’s basically a question of which component is better (simplified answer). I have used both. On my headphone system I have a USB only DAC, so I use that. It is a very good DAC. On my main system I use traditional digital... it sounds ever so slightly better... I mean so little it is silly to talk about.

Without USB isn’t the clock in the Node 2 running the show?

The master clock in the RME DAC is always running the show. It reclocks each digital signal you choose. S/PDIF is high quality and the most practical format to use.

I'm not doubting what you are saying and maybe I'm not reading this correctly from the RME manual under 14.1.2........

" With USB the internal clock is used, with SPDIF the external one".

Isn't that saying if SPDIF the RME does not "own the clock" ? 

The answer is very simple.  You have to listen to your system, using various cable connections and decide what sounds best to you.   There is no correct answer for everyone.  

I decided on a music streamer with BOTH USB and AES/EBU digital outputs to my DAC.  I listened AND listened to both USB and AES/EBU connections for several weeks.

After weeks of switching back and forth, I prefer the AEB/EBU connection from my Aurender music server to my DAC.   To my ears, the music sounds slightly better using the AES/EBU Connection.   

Without USB isn't the clock in the Node 2 running the show?

Yes, but:

1 - You can't put USB in the middle and have it magically control the output of the coaxial cable.  The coaxial signal (or optical) is one way only. 

2 - The only reason this was ever needed in the first place was to improve upon mediocre clocks in the transports by replacing them with the superior clocks coming out in the DACs. So, if the transports had perfect clocks, asynchronous USB would never have been needed.  These clocks are now better than they used to be.

3 - There are clock regenerators, like Wyred4Sound's Remedy, and it does work and it is effective but only up to a point. It works a lot better with old DACs than new DACs which have better clock locking circuits.