Stax amplifier vs Stax adaptor

I’m wanting to know what the difference in sound quality would be between a Stax amplifier and a Stax adaptor. The Stax seem to run happily on just a few watts, from a set amp with an adaptor. I’ve never tried a Electrostatic amplifier, nor do I understand how one works. The after market of an adaptor seems to be minimal, while a used Electrostatic amp seems to command substantially more.