I can answer my own question here.
I checked in today for SQ232, with my KF number in the booking. I had my printed card, print out of the status match email, and print out of Star Alliance gold benefits and lounge access policy in case they were required. All I needed was the card print out (screenshot as they need the number).
At check-in I used the business line as an economy passenger. The printed card was all they needed to see. They gave me an express card.
At the lounge, they needed to manually check me in and needed to look up the airline code (O6) but it was fairly straight forward.
At the gate I joined the business line, showed my printed card and was invited through.
One wonders how many of our forum members have already done this in Sydney as it seemed like it happens frequently.