The segment of the house/dance/club scene I casually intersected with in the early 90s seems to have been big into Atari STs

Yup, the ST was the DAW of the 80s/90s. The onboard Yamaha soundchip was rubbish, but it had built in midi ports that could be connected to various synths, drum machines etc. The Roland JV-1080 and Korg M1 were used by many EDM outfits of the 90s. A lot of the sounds on Insomnia by Faithless was done on the JV-1080. Jean-Michel Jarre used the ST extensively as well.

Visage Fade to Grey using an ST and a Clavia Nord

https://www.youtube.com/watch?v=JRRJJ9UkThU

Friend of mine was a keyboard player in a symphonic black metal group in the late 1990s (not exactly techno, but it's still music 😉 ) and he wrestled and got hopelessly frustrated with a Terratec EWS64XL which theoretically should have been able to fulfil all his MIDI and sampling needs but in practice never quite was. I think he just fell back to default sounds from his keyboard eventually...

The jv1080 was the most used synth of the period, and everyone used it. Amigas were common, so were Macs. But pcs were too. At the high end it’s possible some pros were using next machines. It was really all over the place computer wise. If you go watch videos or see pictures of many game composers, they tend to be using pcs, Macs or amigas, hard to tell what was overall most popular.