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. 
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Interestingly, I followed the same path as “almarg.” I bought a pair of Stax Lambda Pro headphones in 1990, powered by the Stax SRM-1, Mark 2 (with the ED-1 equalizer). At some point, I sold all that and upgraded to Lambda Signatures, with a Stax SRM-T1S. Since then I bought a pair of Stax 009s. I saw an SRM-T1 here on Audiogon, so I bought it as a spare. I’ll skip all the audiophile description of the sound except to say that the SRM-T1 and T1S are far superior to the sound through the SRM-1, Mark 2. The only difference between the T1 and the T1S, is that the S has a balanced input, which I use.
I haven’t yet gotten myself an SRM-T1 for my Lambda Pros (still using the SRM-1 Mk.2. Hey, it’s not THAT bad ;-), but in addition their great sound the Lambda’s are also usually comfortable, unlike some earlier Staxes.
I still have  my Lambda Pro headphones and SRM-1 Mk 2.

Use them when my neighbors complain about my 2 channel stereo. 

Classical CDs only via Bryston spinner and preamp.