New Stereo/old Alternator

[plusnone]

I'm working on upgrading the stereo in my 1987 325, and want to know whether I'm going to overload the alternator. If all goes well, I plan to be running:

-1x Audiobahn 600W RMS Amp powering two Alpine 10" subs
-1x Audiobahn 400W RMS Amp powering two Alpine 6"x9" rear speakers
-1x Pioneer head unit, rated to ouput 22W x 4 RMS

I don't fully understand Ohms (and Ohm's law), but from what I've been reading, I should set up the 6x9s to draw 100W each at 4ohms. Does this still mean that the amp will be drawing 400W?

From the manual, my alternator ouputs 80 Amperes at 14 Volts, for a total of 1120 Watts. My air conditioner does not work, and my headlights are original (although I don't know how much current they draw). Am I correct in thinking that if my system isn't running at full volume all of the time, I should be safe with my current alternator? If it matters, my starter is brand new, but I don't know how much power it draws.

Thanks for any advice,
-plusnone

[PMB]

Unless you are planning on going into competition you will be fine. The stock alternator is more than adequate. However, you should consider installing a 0.5-1.0 farad capacitor. This acts as a buffer by storing the power that is required for sudden hard dynamics, thus helping to protect the battery by smoothing it's power delivery requirements.