This has nothing to do with Bryston products, just a general observation and answer to "will it work" question in general.
An amplifier or preamplifier supplied with a 120V 60Hz only power transformer might not give satisfactory performance with a 240V to 120V step down transformer in a foreign country using 50Hz AC supply lines.
The issue is that at 50 Hz, the transformer and power supply are being replinished slower, only 50 times per second as compared with 60 times per second in the USA. Thus the energy supply to the circuits is reduced by that factor 50/60ths of normal, or about a 16 percent drop in available energy per unit of time.
Bryston, along with other high quality manufacturers, furnish power transformers with "oversized" cores to make up for that difference when the equipment is being used on 50 Hz supplies.
However, a 120V 60Hz only transformer will have a smaller core and less energy delivery capability. It will be fine on 60 Hz supplies, but might suffer with the extra demands of 50 Hz. That 16 percent less available energy from the supply line could cause transformer overheating and voltage drops to the circuits. If the headroom is tight, regulated supply circuits could stop regulating. These would have an effect on musical performance.
So, if you are taking equipment made for 120V 60 Hz to a country where the supply is 240V 50 Hz use caution. An external step down transformer might not solve your issues.
Make sure the equipment does have a 50/60 Hz transformer core first.
Frank Van Alstine