Edo,
I'm using USB to USB. A Bel Canto engineer told me
by phone that with a Mac, USB is best, so haven't even
bothered trying optical. ( Maybe USB is best with Windows
too, I don't know -- and I don't care. ;-) )
As I inferred in my previous post, I tried lots of fussy mussy
and complicated stuff, to little avail and at significant expense.
None of it was worth it, that I could *hear*.
Hard to beat a $5, 6" USB cable for simplicity. :-)
I currently use only the hard drive in the Mini --
I ordered a 120 GB drive upgrade when I bought the Mini new,
which holds about 400 CDs in Apple Lossless format.
That happens to be enough for me, for now.
I own a Newer Technology 500 GB 'mini stackable' drive
that I use for other purposes, but it would be a little too noisy
for my tastes as an add-on the Mini server. I've read that
quieter Mini-stackable drives exist but I can't advise
which though, I've forgotten.