Here we go... I do audio tech work up here at school as a job, and this is what's the dealio
...
When you wire speakers in parallel, which is the standard way of doing things so that your phase angle and voltages play nice.. ( i'm trying not to explain 6 months of circuits class in 30 lines ) ... your impedance goes down.
the relationship is ( R1^-1 + R2^-1 ... )^-1 ...
so if you put 2 8 ohm speakers in parallel you will get 4 ohms impedance seen by the amplifier, which is what you care about...
Amps will all have an impedance rating, DO NOT EXCEED ( that is, go lower ) it. If you place too small a load
on the amplifier you increase the amount of current which the amp is required to source...
and it gets hot, sometimes stuff melts...
The above is probably already known....
The next thing is when you drive a speaker
too loud w/ too small an amplifier your
nice sine wave shaped sounds will
square off at the top and bottom, this is called clipping... and this is what kills speakers. Basically, the cone in the speaker will hit the physical limit and sit there for a bit, and then snap back... that's bad... its a good way to tear the cones and maybe crack a magnet or 2....
With those three drivers, i'd probably be inclinde to buy multiple amps, i think you'll be happier, and probably spend less money. Forgetting money for a sec, the
best way is to get 3 amps, one for each, which will cost tons, and you'll probably need some power distribution stuff for the car power system, like a cap or 2...
More realistically, i'd probably get a 400x2
2 ohm stable and bridge it for 800x1,
put the 400 and 600 on there...then wait to save some cash up for a 600x1 and use that for the 1k driver.
You have options, basically its about how much you want to spend. Last winter we put a 600x1 and a 1200w sub in my friends car,
we had to turn it down so it wasn't painful...
or drowned out the nice focals he had up front.