Think of these pretty portable players as the lovechildren of TiVo, satellite radio and the iPod. They allow you to record your favorite crystal-clear satellite programming TiVo-style and then listen to it later on, wherever you are. Although these wearable units are not themselves satellite receivers-they have to be docked to receive and record content-the XM Samsung neXus and Sirius S50 have two key advantages over their antenna-outfitted relatives: They´re half the size, and you can upload your MP3 and WMA files and mix them into your satellite-radio playlists.