Let’s take a look at where we are today and then what we can do about it.As of this post the biggest limitation to changing the audio system in your 100 series cruiser is the head unit in the later model vehicles.In 2002 (2001 for LX) Toyota began installing a touch screen navigation systems that incorporated the climate control interface.
If you have a 1998-2001 100 series your life is simpler.
The quality of the 100 series audio is passable at best and if you are used to high fidelity then it’s downright useless.
All of them will require some poking around behind panels and some wiring.
Because these head units have the climate control interface there isn’t a super clean way to upgrade the head unit.
There is a project that is undertaking the wiring interface for such a conversion.