Third time I digitized my music collection I'm using flac (first was ogg vorbis, then 192k mp3). But my mp3 player won't play a flac file. So I gotta convert files to mp3 before popping them onto the ...

Digital sound is nothing more than numbers. What separates one container from another is how those numbers are packed, how much data (if any) is thrown away, and which devices understand the result.