Pardon in advnace but I'm trying to learn my new GPS and it's capabilities. I have a Scala Rider and Zumo 550. When I listen to the radio on my Scala (not going through my Zumo), it sounds great. When I listen to a mp3 from a SD card in my Zumo, it sounds really terrible. Is there a common error I'm making? The mp3 is a good quality file and my helmet speakers are good. If it's a matter of the Zumo's audio player, my next fear is that if I subscribe to XM, when I get my antenna, it will sound poor like my current mp3 rather than good like with my Scala's radio. Anyone been where I am and can help?