Thanks for the explanation Antoine! I must admit to being a bit baffled as to why the Mutec was drawing USB current, but reading your post I can now see the logic in this approach. As for burn in woes, I think I almost fried the poor little microRendu on Tuesday, plus it's had quite a few listening hours on it now. I note Mutec state that their kit does not require burn in time, I guess the 'pro audio' market target customers are less prone to worrying about this stuff!
1000 Pro - KEF Blade - iFi Zen Stream - Mutec REF10 - MC3+USB - Pro-Ject Signature 12