An easier way to burn Dreamcast discs, (as someone who owns a Dreamcast), is just to use imgburn, with a plugin available on the website
Step 1: Supply imgburn
https://www.imgburn.com/index.php?act=download
[MAKE SURE TO USE MIRROR #7]
Step 2: Supply the plugin
Scroll to the bottom the first link page until you see "Padus .CDI File Mounter v1.0.0.12"
Click the download button
You'll get a .zip file
Unzip it, and place the files inside the imgburn root directory (default is "C:\Program Files (x86)\ImgBurn")
Step 3: Open imgburn and burn discs!!!
Super simple guide and doesn't require using *slightly* complicated methods!