Navigate to one of your music files (one that won't play); then click on the column headings, and choose to add the "Bit Rate" heading in order to display bit-rate info. Alternatively, do the same thing in a media player, such as iTunes, Windows Media Player, Media Monkey, etc. Find out if the bit rate is too high for the Denon (depending on file type). What file type are your music files--aac, mp3, wma, wav, flac, or ?????
You determine the bit-rate when you rip a CD, or it's predetermined when you grab a file from the Internet.