I'll use the following link and manual at link. http://shop.panasonic.com/shop/model/TH-42PD60U?t=specs&support#tabs

I see two possible connections.
Audio Output 1 rear
Digital Audio Out 1 (optical)

To see if there are more details I'll read from http://service.us.panasonic.com/OPERMANPDF/TH42PD60U.pdf

As you can see the prog output is only enabled on certain content. "When receiving digital channel signals, all digital formats are down-converted to composite NTSC video to be output through the PROG.OUT

But it is possible that these are broken in some way. Do you have any means to test the optical output?