Hi Pete,
It's typically not possible to monitor the incoming audio to the Intensity Pro from the system audio, unless this is implemented by the software developer. However it typically is not. When you are capturing with the Intensity Pro, the audio will loop through to the card's outputs; both on RCA and HDMI. I've heard of customers looping the audio from the RCA outputs back into the system audio, and somehow monitoring it from there, but I've never tried it myself, so couldn't say how well this might work.