Yamaha HS7 (230V/50Hz) used in Brazil on 220V/60Hz — is it safe? Also investigating a low-frequency resonance

I have a Yamaha HS7 studio monitor whose rear label specifies 230V / 50Hz. In Brazil, the mains frequency is 60Hz, and I would need to use a step-up transformer to get from 127V to 220V. Yamaha support has told me they cannot guarantee proper operation under these conditions, but they haven’t clarified whether 60Hz can actually damage the monitor or cause functional issues. Has anyone with technical knowledge of the Yamaha HS series or powered studio monitors dealt with this situation? I’m also investigating a low-frequency, resonant “whoom” sound on a specific guitar note. The sound is present in the recording itself, but it becomes more noticeable through the HS7. Any technical insight or experience would be appreciated.