In demos, there are sometimes coordinated sound and visual effects. For example, in Elevated by rgba, there are lights in the sky that are coordinated with the notes.

Is the current state of the music system visible in the pico8 ram somewhere?

You can use some undocumented parameters of stat(n) for this

16..19 gives you the sfx currently playing on each channel or -1 for none
20..23 gives you the currently playing row number (0..31) or -1 for none

Note that the row number may not be very precise depending on what is going on with the host operating system's audio mixer. Also in the case of the web player which needs to have a large mixing buffer, the result is often slightly earlier that what is audible.

(p.s. you might want to change the post category to pico-8)