Mp3 Music Cuts Out During Playback On Itrek Mi3000-why?

I bought a Sansa Fuze MP3 player and Memorex iTrek Portable Speakers Mi3000 together for my husband's birthday with the idea we would take it out in our boat.  We've used it twice, and each time we play it using the Line In cable, the music cuts out in the middle of the song. At the beginning of each song, the song plays but you can't hear it through the speakers until five or six seconds into it.  I tried deleting and redownloading  the music on the player, and replacing the Line In Cable, but it continues to randomly blank out.  We are sooooo disappointed because when it does play, it sounds good! Then we called 954-660-7100 for the Memorex Customer Service and found it to be a fax number.  My husband just called Fox International and they told him that this portable speaker unit was not made for an MP3 player. LOL! Why didn't the ad say so when I bought it?  Why did it come with a Line In cable if it wasn't MP3 compatible?  Is there anything I can do to make it work?