@alex_free, allow me to be the first poster to express my thanks and confirm that your handiwork is faultless.
Following the instructions to the letter on my 2011 13" MBP under El Capitan, a CD-R was burned for me at 8x on the internal optical drive.
I placed the burned disc into the Dreamcast and it was time for the moment of the truth.
Hooray! It has reached the boot screen: so far, so good.
The emulator has loaded.
Let's pick a game and have some fun.
This emulator works perfectly! I no longer need to seek out a Sega Master System and the cartridges at inflated prices (due to retro greed) because I can play the titles on the DC for zilch and with the advantage of much greater flexibility and options. I'm now in a situation where the sky is the limit in terms of what I can explore on the homebrew scene and retail DC games because creating a bootable CD-R from a CDI file is an automated cakewalk.
Alex, thanks so much for your continued efforts on countless fronts that have brought us so many boons in the Mac world. Just a week ago I had no idea that I'd end up owning a Dreamcast and now look at what's available to me without having to mess around with one of my Win boxes.
Astounding!