I did an install on a XLS a few weeks ago.
The system consists of the following:
Cheap ass HU (soon to be replaced)
Kicker 6" co-axles
Pioneer 12" sub in prefab enclosure
Jaycar 4x100wrms Amp.
The speakers fit with a thin MDF spacers
The standard space is 2 x DIN, but you shouldn't have problems finding an AU pocket. I got one from the car audio store that I bought the speakers for about $15.
The amp was installed under the drivers seat. There is a bit of room under it as the Jaycar amp is quite large. You could put a stacker under the other seat.
The sub sits behind the drivers seat facing forward. When the car is closed you can't see it, but it should be noted that the windows are tinted.
I will try and get some pics this weekend.