Hi everyone!
Long time lurker here, chiming in because I think I might have something to contribute to this thread.
Just like for the OP the perceived difference between Logic and Cubase had been bugging me for some time, so last year I bit the bullet and performed the null test. Unfortunately I don’t have the sound files any longer so I can’t submit any "evidence", but I will walk you through what I did and you can decide.
I loaded up a strings patch from Albion One in Kontakt in both Cubase and Logic on the same Mac computer. I reset the round robins to ensure the same wave file would play when the note was triggered. Pan law was set to the same in both DAWs and there were no automation or additional effects applied (Admiral Bumblebee has shown that these are indeed different between DAWs).
I then captured the resulting audio outside of the DAW using Rogue Amoeba’s Audio Hijack software. This produced two wave files, one from Logic and Cubase respectively. I imported the files in Cubase and phase inverted one of them.
At first they didn’t null, there was still some sound coming out from the stereo master. I thought that maybe there was a fundamental difference after all. But when I looked more closely at the two original waveforms I noticed that the Logic one was ever so slightly lower in amplitude.
So I increased the level of the Logic file with 3 dB and presto, now the files nulled! Well, at least the stereo master level peaked below -110 dB, which I think was due to the difficulty in lining up the waveforms optically, even at max zoom I was probably a couple of samples off.
So IMHO Living Fossil is correct that the difference is due to the output levels, and this impacts the perception. I had always thought that the mid range in Kontakt in Cubase was slightly clearer, now I am confident that Cubase and Logic sounds the exactly the same and have opted for Logic for workflow and stability reasons.
Of course, if anyone else could take the time to perform a similar test that would provide independent verification and we could bury the topic once and for all.