Ed is right, they have had these out for quite a while. I've got two three-way units at my place. All they consist of is a three way crossover, isolation transformers on the inputs, diodes on the outputs, and plugs so you can connect christmas lights of whatever suits you.
For the apple pro speakers, it should be very easy. For now, lets just hook into the subwoofer.
At this point, I warn you, I'm not responsable for whatever you do with the below information!
Take a volt meter, or if you are more fortunate, a scope, and hook it up directly to the speaker. Put the volt meter on AC. Find a song that bumps. If you have a way of generating a 60hz tone, that will satisfy the volt meter greatly.
Take your reading (in volts of course) with the system cranked up to the max. Lets pretend you got 16 volts, for our example.
We're now going to use Ohm's Law to figure out the correct resistor.
The first thing to figure out is, how much current will the light be drawing? To keep things as simple as possable, lets work with a low-current device, such as an LED (as apposed to an incandesent light bulb). A higher current device will pull more current from the audio amp, and possibly distort the sound (there are ways arround this, for now, lets keep it simple).
Four RadioShack 276-316 High Intensity blue LED's should be cool. We'll wire it up so two go on the first phase of a wave form, and the other two go on the seccond.
Because audio is (idealy) an ac wave form, and LED's act as diodes, they will naturally light for only one phase of the waveform.
This also means they only draw a signifigant amount of current for one cycle.
Thus, we'll just add the current for two LED's together.
each LED is 20ma, or .02 amps. We'll place two in series. (thats -->|--- -->|---). So, .04 amps.
Now, Ohm's law states that E=IR. Or simply, Voltage = Current times Resistance.
Now, take the voltage you measured, and find the difference between that and the required voltage for the LED. The above mentioned blue LED handles 3.7 to 4.5 volts. For a safty margin, we're going to use 4 volts as our number.
So... if you measured a peak reading of 16 volts, and the LED wants about 4, your difference is 12 volts. (duh).
so...
12 = .04 * R
Divide both sides by .04
12/.04 = (.04 * R)/.04
R = 300 Ohms. That worked out nicely. Your result will more than likely be something like 372.04 or whatever.
But wait, you don't run your system at peak volume at all hours do you? (well, if you're 'kilowatt' you might...)
So, rather than using the 300 ohm resistor, lets go variable!
You're not likely to find a 300 ohm variable resistor. But a value arroud 1k or 500 ohms may be avaliable.
Bare in mind that 'Audio Taper' means the resistor's variableness is logarithmic. Not linear. This may not be desireable, though it will work.
Here is the complete ascii diagram for our circuit:
Code:
[apple pro sub]
(+)--/\/\/\/\/\---NC
^--------------|
(-)|-->|-->|-------------|
|--|<--|<-------------|
key:
(-) Minus terminal
(+) Positive terminal
-->|-- LED, Anode to Cathode
--|<-- LED, Cathode to Anode.
--/\/\/\/\---
------^ Variable Resistor.
NC = Not conected
So basically, we put two LED's in series. Then two other LED's in series. The place those circuits in parallel, with one circuit's polarity backwards. Connect one end of the resulting circuit to the negative terminal of the speaker. Connect the other end of the circuit to the middle leg of the pot. Connect either outlying leg of the pot to the speaker's positive terminal. Leave the other leg as it stands.
Good luck, enjoy, and no, I won't buy you another speaker.
--kilo
, but it seems possible. I'm not sure how speakers work, but I assume the current varies through out a song ... and maybe if the light was hooked into that it would cause the light to flicker? Or maybe I'm completely wrong! 
