See I knew it was a silly question :) A few minutes ago I converted the otf files to ttf using font forge. That appeared to work, but it seems the ligatures are gone. On top of that the ttf version of the font did not show up as a monospaced font in my code editor. I might have done something wrong though as I only dabble a bit with font forge.

Then I just did what you suggested, install the otf instead (d'oh) Now the fonts do show up as monospaced font. But my editor does not display the ligatures. But at least it is usable.