I have not heard the Stenheim Alumine 3, but I own Amati Traditional (see my virtual systems). From reading about the Stenheim… they are as different as you can get from the Sonus Faber, both sonically and aesthetically. From the descriptions the Stenheim are a Magico wanna be.
Sonus Faber’s thing is natural beauty in both sound quality and their look. They are simply the most beautiful speaker I have ever seen… or heard.
If you are an older like me, I have gravitated to natural musical systems as I got older… ones that sound like real music instead of pinnacles of technological achievement that don’t really sound that good. My previous system highlighted the venue and mastering over the music… it made many recordings sound bad. My current system draws me in to the music and I forget about the system. That is what Amati does… it’s about the music… getting out of the way. So now that I am retired I listen three hours a day… and have to be dragged away from my system.
I’m guessing the Stenheim are faster and a bit more detailed and will let you hear the third violinist move his foot… but not suck you into the music.