Hello,
The fact is works on other devices still leads me to believe that this is a printer issue and not a software issue. If the same code is sent to multiple printers I fail to see how this same code can produce different results.
PlanetPress does not use drivers, we generate our own Postscript code and bypass windows drivers. I don't think the problem is driver related.
I will never say it is impossible it is our software but it looks to me printer related.
However, I have 2 possibly solutions although neither of them are really pretty.
1) Duplicate the text and stack them. This should give you a more "full" feeling.
2) Use a very small scale in the PressTalk before the objects that show text. This will increase the size and should make it appear darker. I would suggest scale(1.02,1.02)