I did the codec dump, and while I was running Linux, I tried making some sounds.
Nothing. I then hooked up my new cheap set of amplified speakers to my iPhone - nothing (!)
I plugged headphones into my Hackintosh (still running Linux) and was able to get sound.
Rebooted back into El Capitan - and with headphones I had sound!
Bought a different brand of cheap speakers from a nearby Best Buy so I could return them if necessary - and they worked fine with my iPhone.
They also worked OK with the box when I boot into El Capitan - but there is a really terrible hiss when nothing is playing.
(I'll research the forum for this issue when done with this message)
I rebooted into Linux - and the sound through the new speakers is crystal clear - with no annoying hiss - so it's definitely something with my OS X install. Sounds almost like the gain is all the way up or something...