[DVD-o-matic] BluRay Conversion too bright

Today I had to play a commercial BluRay, converted to DCP with MakeMKV and DVD-o-matic (0.89). It turned out much too bright on our Sony SRX-R515. This is a fairly new installation and the calibration is certainly perfect, I never see any issues on commercial DCPs and trailers. Initially I thought this was just a Gamma issue, but I found out that on this machine the Gamma for DCI content is already maxed out at 2.6, I can only set it lower. It was a straight conversion, no intermediate conversion, no filters, I chose REC709 in DVD-o-matic, and on the Sony projector our standard flat DCI preset. It wasn't subtle - about 30% of the movie showed decent contrast, most other brighter scenes were very milky, and in darker scenes shadows were torn into noisy dark green and blue. Detail was very good actually, I chose a no-rescale conversion (flat no stretch). This projector actually has a brightness, contrast and color saturation slider. Usually I never touch these things, because on a properly calibrated machine everything should be okay after the calibration. The DCI flat preset had these sliders in their default positions, which were 100 for contrast, 50 for brightness, 50 for saturation. I could actually fix the problem by reducing brightness to 30 and reducing colour saturation to 45. I played the BluRay in parallel to the HDMI input configured to REC709, switched back and forth and it matched quite well. I did not have more time for perfection, there was still a slight color shift between the two, but it was okay. I guess I will have to send my BluRay calibration disc through the same conversion to find out what is going on there. Any ideas? - Carsten