Users of the Beosound 5, what kind of audiofile format do you use? There're lots of formats, and as we're interested in high-end audio, I presume everyone uses lossless formats? Is there an audible difference between FLAC and WAV? From what I read on the internet FLAC still uses some sort of compression? Who can shine some light in these matters?  And how is SACD used in this (non-disc) way? Is the beosound 5 capable of playing SACD files?

The Beosound 5 works best with WMA lossless as this is the only format that supports gapless playback.  I personally use a combination of WMA lossless, mp3 and acc (I've been too lazy to losslessly encode all my music).

With respect to audible differences - lossless is lossless.  Lossless compression algorithms compress the music on the disk, but uncompress it when sent to the DAC.  Lossless means that no bits are lost or changed in the compression/uncompression process.  Assuming there are no bugs in the code, all the bits are the same when presented to the DAC (which turns the bits into music) regardless of the original *lossless* format.

Stan