Yes, Tetenal's powdered kit was marketed as a "Press" kit.
I have used the Unicolor powdered kit many times over the last thirty years. I've always had decent enough results, even playing with ECN films.
Ammonium thiosulfate is indeed a powder, which is what makes up the liquid versions. I have some in a jar. When Tetenal or Unicolor use it in a sealed mylar envelope, there are no issues. Just follow the directions.
Can't speak to the Tetenal, but the Unicolor comes with separate Blix A (fixer) and Blix B (bleach) envelopes. Unless PE or someone of knowledge can tell me otherwise, it seems that one could mix separately and use sequentially.
I have a Unicolor order coming from Freestyle. My intention is to mix part of it as usual, but keep most of the developer in powdered form and use it as a diluted C-41 per David Lygra's experiments. Can't do that? Maybe. Maybe not. It's just fun, not religion.