May use a step down transformer for HI-End ?

Chances are a CD player, tuner, and the like (small units) will work - look at the rated consumption, it should be inside the transformer's rated power, preferably below. An amp, however, will not. Some components can be converted relatively easily - if they have jumpers/switches for that purpose somewhere at the AC input. In this case, you may even be able to do it yourself. Others, however, need either a total replacement of the transformer (if you can find someone to do it) or a serious step-down transformer like the one here. I have not used one myself, so I don't know how they work with hi-fi gear - if you get one, let us know.

You have a bigger problem than what is mentioned above. You need 60Hz for US equip - in Europe it is 50Hz only. A transformer WILL NOT do this conversion unless special circuitry is added to the transformer (called a cycloconverter). So, check to see if what you have will also convert the frequency. I think you may need a product specifically made for your application. However, there is also a chance that some American equip will work with 50Hz. I would look into this very very carefully before plugging anything into the socket.

You don't have to worry about the 60hz vs 50hz problem, unless you are powering a motor (turntable using an AC motor). Also might be a problem using a tape deck with AC motors. Most equipment, including those with motors, use the AC current and convert it to DC, even for the motors. I ran my Alex TT on 50Hz 110V (converted from 220v), with no problems, because its moter is a DC motor.