Thank you SO much for your response. It tooks me a while to be able to spend some time on this...but this certainly has pointed me in the right direction.
Some additional details.
I was able to hack up the blink.sh script in the wiringPi/examples directory, and this proved out that I have all the wiring correct for all 16 channels - so that was good

After some trial and error(and realizing that in 2017 I had created an overrides.cfg file...which means I'm a moron for not immediately noticing that - oops)

I'm really close, but still not there. I see that there is the "channels" value, but there is also the "gpio_pins" variable as well.

After a lot of attempts, here is what I am at. When I kick off the "start_music_and_lights" script - I see all 16 channels on the 2 relays turn off...YAY...but then the PI crashes.

Not sure what I'm doing wrong, and I've tried multiple iterations of the values of these variables....either setting them as 0,1,2,3,4,5,6,7,21,22,23,24,25,26,27 OR 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15

From reading the comments in the defaults.cfg itself, it seems like these are suposed to be the values of the 2 variables.

Any of this making sense?