My radio has been cutting out along with my two 12 inch subs, I took it to circuit city they said its my alternator not charging enough. What could it be??

I have a kenwood KCD radio, 600 watt kenwood amp and 2 MTX subs 12 inch

 

you might want to turn the gain down on your amp. I have 2 Eclipse 12 Fosgate 600w amp once i turned my gain down my speakers stopped going out but my dash only went out once.