My system is set up the following way:

- tweeters mounted on the doors, just below the side-mirror controls
- midrange in the door enclosures
- bass tube in the rear hatch

The rear towers are useless -- all they could accomodate would be some
6x9's, which wouldn't provide good bass and sound terrible in general.

I highly recommend a Bazooka bass tube, which has its own enclosure and
is designed to be pointed into the back of the cabin, using the whole
rear of the interior to project into the rest of the cabin.  It's
fantastic sound.  I also suggest separate amps to drive the low-end, and
a crossover on the midrange speakers and tweeters -- removing the bass
frequencies lessens the load and stress on them, giving them more power
for producing clear-sounding mid's and high's.  For a two-seater car you
really shouldn't consider putting any mid- and hi- range speakers in
the back.  The above arrangement I described is perfect for the CRX.

Here's a diagram of my setup:

   HEAD UNIT
       /
   [pre-amped
    output]
     /
     -> CROSSOVER --[mids&highs]--> 3548 AMP, --> Boston Pro mid/high
            |                       60w x 2     (has its own crossover to
            |                                    sends mids to the 4.5"s
          [lows]                                 and highs to the tweeters)
            |
            v
         3541 AMP, ---> 8" Bazooka tube
          100w