Can US 220v be used to power foreign 220v pieces?

So long as the gear can accept both 50 and 60 Hz frequency, yes (most modern gear can do this). However, most 220 VAC 60 Hz in a residence is used to power the stove and electric clothes dryer (furnaces too, but that's rare). Those can be noisy, so you could have an issue if running audio and appliances at the same time.

Good luck & happy listening!