According to Denon UK website ( http://www.denon.co.uk/site/popup/index ... start&ver=
) the Denon 3310 supports "MP3, WMA (DRM), AAC (not DRM), WMA Losless Transcode, FLAC, WAV" formats.
I do not know why they would play in WMP and not Twonky. The lossless WMP files are not copy protected.
I'd use FLAC, but FLAC playback always arranges the tracks in alphabetical order, even when I number them