As mentioned before, I wasn't quite satisfied with the sound of the stereo.
It definitely needed a little more bottom end to complement the front splits.
I was lucky enough to get hold of a cheap second-hand 10" subwoofer in a box
(for $30) that would fit OK in the rear of the 180sx. It wasn't anything
special, but as I said before, my old ears can't really tell the difference,
Of course, to run this sub, I had to decide whether it would be possible
to run it off the head unit, or purchase an amplifier. I decided that even a
10" sub is likely to need more power than the head unit could comfortably
provide. Looking around I managed to buy a new Sony 222W amplifier for $120
from Rick Hart. This amplifier was about as ideal as you could get for my
application. It was cheap, powerful enough (especially when used in bridged
mode) and it was cheap. I also knew it was guaranteed to work nicely with the
Sony head unit.
The installation turned out to be an absolute doddle. The previous owner
had left some good quality RCA leads already run between the head unit and
under the passenger seat, along with a heavy duty power cable and earth lead.
It was simply a matter of connecting the existing cables to the amp, screwing
it to the floor and switch it on! A little bit of adjustment to get the level
of bass to balance the front speakers and all done. I'm now very satisfied
with the sound. The additional $150 was money well spent.
Update: The original second-hand speaker eventually died, so I replaced
this with a new cheapie ($39.95) "Fly" brand subwoofer from Supercheap. This
actually didn't sound too bad at all! Unfortunately, this was stolen only a
couple of weeks after I purchased it (the thieves smashing my drivers side
window in the process). This was then replaced with another second-hand
speaker and box, though this time it is a 12". This does have a little more
punch, but isn't quite as crisp as the fly 10"... oh, well...