WMA files tend to sound better at lower bitrates (128 and below) while mp3's reign from about 160 kbps and up. I recommend trying several types of low bitrate wma's on your player and deciding at what point you can begin to hear discrepencies. Currently, I use 96 kbps wma's on my creative flash player which has allowed me to double the storage capacity over the the 192 kbps mp3's stored on my computer without much quality loss. I use the creative media source software which allows me to convert the files on the fly while they are being transferred to the player.