I'm using a 240V amplifier powered by a 240V outlet.
I experimented with step down transformers and while they worked fine, they have the following drawbacks/considerations:
1. they can hum.
2. The are not efficient. You may lose 10-20%. Not a big deal unless your load is high (mine was).
3. You need to buy an oversized one to supply an amp. My amp is 400 watts and I bought a 2000W transformer. Still, you have to worry about output impedance.
4. A better solution would be a PS audio or similar power supply. They have basically zero output impedance so there is no impedance current limit to your amp. unfortunately, they don't seem to make them that change voltage. they only offer 240 in / 240 out and the same for 120. You might use a transformer and a regenerator but I didn't try that.
5. It is a good excuse to run a new circuit to your stereo system and have a dedicated line. It is no more trouble to run 240 than it is to run 120 and of course you have dedicated 120 lines for all your accessories.
6. A 240 V amp has the advantage that is uses half the current. So in general you can get by with one size smaller wire size for your power and cords.