Mike's PCjr Page

Correct me if I'm wrong, but doesn't the PCjr's monitor/display port also have sound?
Wouldn't it be possible therefore, to modify Texelec's CGA/Serial breakout board to have a mono sound port. Possibly and RCA or headphone jack?
https://texelec.com/product/ibm-pcjr-cg ... out-board/

The PCjr itself already has the exact thing you're looking for. The RCA jack "A" is the same as the audio on monitor port "D". (the audio is also used in the RF port T)

And furthermore, all three of these are the same sound output as seen by the mux chip, so this would only be useful if your RCA port is broken. But then you'd just fix the RCA port.