Stem volume clipping when remixing in Cubase

[klubertanz]

Hello fellow forum users!
I want to adress an issue which I have come across too often now. After extracting stems on a project I assemble them in a new file to test if everything is ok. It is, except the volume of the combined stems adds up too high and even peaking over 0dB on the master channel. I can of course turn the master down and be done with it, but I would like to deliver better technical quality to the production houses that I cater to.
I´ve tested this (the re-assembly) in Cubase 6 and 10.5 as well as Audacity. Same result. No compression or other dynamic-altering fx on the master when exporting, I´ve taken great care to only effect the stem groups, nothing else. The individual stems are fine and well below the danger zone. What puzzles me is that I cannot make them play identically to the 60+ tracks original files they are derived from (where I am keeping headroom on the master of course).
If somebody would have advice for me, this is greatly appreciated. I´ve delivered a lot of stem breakdowns for cinema and TV in the recent years and never got complaints (they probaby put the music on its own bus and attenuated the volume to taste anyway), but I still feel I could do a better and more professional job with this.
Have a wonderful day everybody, best
Michael