The PIC have only 2 comparator if my memory serves me well, you if you need 3 different trigger source working at the same time you will need to add some external stuff... not really interesting.

Here the ADC solution have it's own advantages. It will allow as many trigger source as you have ADCs. ALSO you can implement software threshold on EACH audio band (low, mid, high)

well configured and speed optimized (clock source, acquisition time), ADC are not so slow, and BTW, we don't talk about something really timing critical... it's visual effect on audio. nobody will see the difference in a few ten or hundreds uSec of latency

So you build a modern version of the old-timer 'color organ' ?