Audio Systems: Hooking up an external amp, line level inputs, amp volume

Question
Hello.I need help hooking up an external amp to my yamaha home amplifier.My yamaha is my main amp.I would like to increase the power output by hooking up my kenwood amp to it.My yamaha manual says to hook up the external amp to the pre outs in the back of my yamaha.Now where do i hook the other end of the rca's to my kenwood?To its preouts as well?
or to a line in such as cd input?I have tried this methods and nothing seems to work.volume up all the way on the kenwwood as my yamaha manual sugests but i dont notice any difference in volume.shouldn't i notice a change in volume if i adjust the external amp volume?I would tend to think so.My manual says hook up external amp to the preouts and turn the volume to the max on the external amp.it doesnt say where to hook the other end of the cables to.Thanks you for reading this .Bryan

Answer
First of all the volumne level will be determined by the power of the amp and the speakers used.  I can't tell you if the Kenwood is more powerful than the Kenwood.

The connections are as you describe correct.  The Kenwood contains both a pre-amp section and amplifier just like the Yamaha.  In order to control the entire system from the Yamaha, the Kenwood needs to be set up just like an amp alone.  This means that hte volume control on the Kenwood should be at full volume.  The volume level will be controlled by the Yamaha and the signal level at the pre-out will vary depending on the volume level (Yamaha).  You can use any of the line-level inputs on the Kenwood as long as the correct input is selected.

Dan