To be honest Marco the issue of reliable (and inexpensive) storage and backup is the one thing that puts me off getting a Pi to use as you described and I think that Neal has some very sound advice to offer.

Like others, I hadn't realised that dual drive raids were not self supporting and require additional drives of equal size for backup - this knocks this system out of my price range straight off. I have no need to use another device such as Pi to access Spotify or other online sources - I have my Mac/DAC combo for that already.

Storage reliability is one of the main drawbacks of digital systems - and I've lost enough data over the years to take it lightly ...