I think what I've done with mine is similar enough to be helpful
I send the composite video signal from the recorder output SCART via a balun to another screen upstairs and
at the same time watch HDMI on my main screen.
What I found was by set up the composite output exactly as you want, eg wide-screen, letter-box etc., and then switch back to the HDMI settings, the composite setup is not altered, so both settings 'stick'.
hth