The N800's audio chip is pretty good as far as mobile devices go, but without a dedicated quality sound card I assure you you won't be able to hear a difference between 320 kbps MP3 and FLAC, no matter what kind of headphones you use. The only real reason I see for trying to play FLACs is to avoid the hassle of transcoding into a lossy format if your main collection is in FLAC.