I would double check with someone whether that TV takes 720p input on any of the HD inputs. That is a NATIVE 720p set, but it looks like it has done about the most absurd thing possible... it does not list 720p as one of the accepted inputs. This is a very, VERY big failure on the part of any TV manufacturer to not accept the 4 standard video formats of 480i, 480p, 720p, and 1080i.
While I am not sure what your STB has for outputs, my guess is that it includes component and either HDMI or DVI. Depending on the digital connection, you could use the appropriate cable converter if needed... or just use component.
Leprkon, I believe that 'commercial' Pioneer plasmas do not ship with any cards at all. You have to get a component input card and video card completely after-market if you want to make any connections to the monitor.