Click the link to access the owners manual for the SA4200. It talks about re-sizing the video starting on page 57. Your plasma probably also has a view mode to stretch, zoom etc. Between the two, you should be able to fill the screen. Keep in mind, some channels transmit at 720p pillar box and you can not stretch the picture under any circumstance. It will be 4:3 pillar box. Good luck.
http://www.io.tv/pdf/sa.pdf
http://www.io.tv/pdf/sa.pdf