I have a Metrum Adagio which is by far the best DAC I have ever had. I find the Metrum to be extremely responsive to the set up.
The biggest difference to the DAC ($12,000 AUD) has been the addition of Empirical Audio Syncromesh. Steve Nugent from EA has just updated what was a stellar performer to a 7 psec specification. The effect of the Syncromesh isn't subtle and adds improvement is soundstage width, height, detail, dynamics and most importantly renders a very natural and "in the room" sense.
I have compared almost every combination possible and I can say that the onboard Xmos USB in Metrum is not great. What is great is the BNC input. That is a different beast altogether. BNC is the sweet spot and the Synromesh is true 75 ohm. If you can use a good PS - such as an Sbooster, you will never look back. Steve also makes a Dynamo PS which is a modded Paul Hynes - optimised for digital that I haven't tried yet.
I also found that the XLR (as have a few reviewers) sounds better than the RCA.