I'm pretty sure my June 2016 MS75D UHFS was made by s1nn... can't find out who makes it now but I'm hearing possibly it's Burmester
According to Teslatap https://teslatap.com/articles/audio-systems-for-the-tesla-model-s-and-mo... the amplifier is "The audio systems for both the Model S and Model X were originally designed by s1nn. Harman International Group acquired s1nn in early 2015. Harman owns major brands such as Harman Kardon, Infinity, JBL, Lexicon and Mark Levinson. They also produce high end vehicle audio systems for a number of vendors including Audi, Bentley, Porsche and now Tesla."
However; the part responsible for the sound image is the CODEC. On the UHFS cars Tesla recently changed from Dolby to "Immersive Sound" Anecdotal reports are that the new CODEC is amazing.
Yes s1nn was the last I heard as well but hearing now it may be different