(I should know I am a professional musician).
I play piano/synth, guitar (acoustic/electric), bass, drums, sax. I come from a musical family - Dad was a jazz musician and music teacher. We had 3 pianos in the house in constant use, a trombone, various saxes, trumpet, clarinet, flute, guitars, drums, bass, you name it. Either my father was playing one of those, or one of us where playing instruments.
I used to use recordings of real instruments I owned, and voices of my family, for live-vs-reproduced comparisons when checking out speakers.I still use those recordings sometimes to double check through speakers I have at home. (Not to mention, for my job I'm constantly recording real life sounds).
A lot of us here have a good idea of what real instruments sound like. :)
I'm not disputing that the Magicos sound more "right" to you, or that the Harbeths are "more right." No speaker is perfect and we all tend to focus on certain things that sound "right" to us when we choose our speaker.
I loved the Harbeths and bought them to see if I could replace my larger Thiel speakers at the time. I sold the Harbeths because in direct comparison my Thiels struck me as a bit better in almost all areas, mostly "cleaner" and more precise - some of which I think was due to the "remove cabinet vibration from the design" in the Thiel strategy vs the "let the cabinet vibrate" strategy in the Harbeth. The Magicos would definitely, like the Thiels, sound cleaner in the sense of "less box" than the Harbeths.
But, still, to my ears, almost everything sounded essentially "right" through the Harbeths in a way that escapes most speakers - just something about their way with instrumental timbres - whereas almost nothing sounded "quite right" in the sense of "could I believe this is a sax, or acoustic guitar in front of me?" when closing my eyes listening to the Magico speakers. The Magicos certainly presented something "super clear" in front of me, but it just didn't make me believe I was hearing the timbre of a real instrument in front of me. That was true again when I recently listened to a very nice Magico set up at a high end dealer.
That said, when I auditioned the A3s, there were a few classical guitar pieces, and a soundtrack of closely-recorded woodwinds and brass, that sounded phenomenal through the A3s! But then, those tracks tend to make most speakers sound good. But I did leave thinking "those speakers are going to make lots of happy audiophiles."