stere overheats and cuts off

newbie question.please help.  installed kenwood am'/fm/cd/mp3 in my boat  cabin.  Has a special speaker system left over from the home Yamaha receiver (AC). Replaced the Yamaha.  The kenwood drives bookshelf speakers2 forward, 2 middle, and 4 car stereo speakers outside.  these can all play at once or separagely,

Several people say i need an amplifier.  If so how big how does it work?

well lets see if i can help you say 4 8 ohm bookshelf  & 4 4ohm car speakers well  you should use a amp for one of the sets ie the 4 car or the 4 bookshelfs & let the radio play the other set

ps does the radio have room the breath ??? in not maby add a fan the troulbe is if you run the wires together the ohm load is 2.66 ohms make radio not happy & shut down good luck & write back