@TheSheep I've been in Logic for years and use Studio One as well.
I hope this comes across in a friendly manner; I think you're overthinking it man. I can think of a number of very high caliber mastering engineers who do stem work in Logic. It has an excellent audio engine. (Also don't forget that Apple has acquired a number of audio companies in the past. The people they have coding it aren't generic Apple devs, they're DSP engineers who established some pretty great little companies prior to Apple. And considering the money Apple has to throw around I'd imagine they were deliberate in their reasoning of acquiring them...)
One other thing to note - I was sitting in on a webinar a while back with a fairly well established mastering engineer. She's pretty neurotic about this kind of thing... Anyway, she mentioned doing DAW fidelity tests and found Logic to be very transparent and Pro Tools to be anything but. (According to her PT hypes the low end and has a lot of subsonic noise. It's hearsay without the data but I trust her putting her reputation as a a M.E. behind the claims... ((Also worth mentioning was Live winding up at the bottom of the heap... No surprise there really...)) Anyway, the tests weren't just listening tests, she did some analysis as well...)
The main point is Logic does have a solid audio engine, and I've always enjoyed its sound... Studio One and Cubase are spectacular too, but Logic is no slouch by any stretch...
Hey @danny or @Paul have you guys ever done a DAW transparency / fidelity test, or thought about it?