Well I found the datasheet: https://www.scannermax.com/pdf/C506.pdf
Some pretty potty choices of units there, but basically
its torque constant is 1.84 mN/A and MoI unloaded is 1.4x10^-9 kg m^2, which
indicates a few kHz as the frequency roll off point
Given the response is in the audio range, Why not try 16kSPS with an SPI DAC using DDS generation?
Or even a DDS module?
I thought you are wondering the servo driver datasheet. Because we are not trying to drive the galvos alone. I don't know why not to try, I'm actually an astrophysicist who is new in this field. That is why I'm gathering opinions here. To learn to look where. I'll search the options that you said. Thank you!