From the description in the question, the musical devices use individual external power adapters aka wall warts. The statement "probably are from 220v AC -> 9v DC (or 12v)" is not definitive enough to go on.
The recommendation is to measure the voltages at the connectors going into each musical device, determining both voltage, and whether it is DC or AC. Assuming they all use DC is not valid, many devices are powered by low voltage AC from a small wall transformer. Also, the power adapters supplying the musical devices probably have markings indicating their input (110, 220 or universal AC) and output (5, 6, 9, 12 etc Volts, and DC or AC).
Then, simply replace each of the power converters for the DC devices, with "universal" wall warts of the correct DC output voltages. Universal = They work across the entire range of mains voltages, 100-250 VAC being common.
For the devices that receive an AC input, say 9 or 12 VAC, replace their existing transformers with transformers with the same rated output voltage and current in each case, but designed for 110 VAC mains.
Assumed facts : Single phase low voltage electrical utility.
Needs : Has single phase input, 3 phase AC motor controller and 3 phase motor on hand. Can transformer be used to step up voltage.
If you have a single phase transformer (5 KVA) which is rated as step up (or step down) rated for 120 VAC to 240 VAC (or vica versa), can you use said transformer?
Yes, and not much concern for inrush. Part of the fun and learning is just going ahead and trying it. Just be careful. The KVA size could be a problem with inrush current in a home environment (circuit breakers). Use prudence and stand back. You should be ok. Doesn't matter if it is toroidal or not in your application.
Best Answer
A transformer can be both a step up or step down, it just depends on the turns ration and what you consider to be the primary and secondary windings.
What you can do is use a function generator to excite a set of windings and then measure the open circuit voltage on the others windings. This can allow you to estimate the turns ratio and see if transformer will work in your application.
This can give you a better description of how a transformer works and how to do the calculations.