I had an X, and while an improvement from the iPhone 7 - it's no where near improvement of the new phones. The stereo separation is MUCH better on the XS, Max, & XR. I tried all 3.Bass is better, and midrange clearer.
I had an X previously and I have an Xs Max now. There is definitely a noticeable difference in sound quality between the two and the Xs Max is definitely much better. With the X I never felt like listening to anything directly from it’s speakers and always used headphones. With the Xs Max I do sometimes listen using the built in speakers.