The ESL-57 is considered one of the very best speakers ever sold, but won't sound it's best unless paired with an amplifier that can cope with their very low impedance in the treble, and the unusual load they present, which mostly capacitative reactance. Also, the ESL-57's are notoriously inefficient - my own measurement is 85 dB at 1 meter at 2.83 V drive at 1 kHz - and so the low powered SET amps seem unlikely to produce satisfying listening levels. 2~4 watts doesn't sound like enough unless you like listening at rather subdued levels.
It's hard to find anyone discussing a good experience with SET amps and the ESL-57 on the Internet. I found that a modern 845- based SET and also a modern 829- based SET - both zero-feedback designs - did not like the ~0.5 ohm impedance of the ESL-57 in the high treble, the result was a VERY dull sound, almost no output above 10 kHz when driven from either the 4- or 8-ohm taps.
There might be SET amps that work well with the ESL-57, but I'm not aware of any reports of such. If you have access to ESL-57s and a SET amplifier, it's certainly worth a try, but I would not advise spending significant money on a SET unless you know for certain it's a good match with the ESL-57's - or you have a lot of money and just want to give it a try. It's a safer bet to use the 57's with one of the amplifiers that are widely regarded as good pairings.