Same problem I had with my Z2/Panny S97S setup, even though it was 480P, it was still better than a 16:9 configuration with bars.
My new setup using a HTPC and TheaterTek software fits the bill nicely. I know the Z4 can achieve the stretch. Are you sure about the 900? I thought you said some other AVS'rs said it will, are you sure your not hitting the wrong buttons.