What power conditioners can convert 230v to 120v?

I find myself in Australia with a truckload of audio equipment designed for the US.
Check out Richard Grays Power Company. I don't know if it works on 230 volt but he makes an isolation transformer that is a stepdown transofermer - the Substation model that converts 240 to 120v.
I also like their parallel conditioners as well!
Check out the RGPC Powerhouse. This handles 208-240v and converts it to 120v. This is a MONSTER and it is a total solution for power conditioning but it will cost you...
It's msrp is $9000US. It can be had for less.
It is all you wil need for your entire system though
To tell the truth, not much audio equipment (or other stuff) is "designed for the US". It's a global economy, and compatability with the various voltages around the world is usually a design requirement, and an easy one to meet. Transformer primary windings are usually split into two coils, connected in series (for 240V) or parallel (for 120V). A switch or a jumper often makes the change. but some units need to have wires reconnected.

Another approach common in low current equipment is a HF switching power supply which takes a wide range of voltage (like 50 to 260) and 50 or 60 Hz.

Investigate the capabilities of your equipment before investing in a step-down device.