I haven't really done any in-depth experimentation, but I just made a quick-and-dirty attempt at manually installing DOS 6.22 on my 2006 Mac Mini (manually, since the 2006 Mac Mini AFAIK lacks the ability to boot from USB floppy drives). Basically I just downloaded an ISO version of a typical DOS 6.22 boot disk, repartitioned and formatted the hard drive, and manually copied the files on the CD to C:\DOS. It's a bare-bones installation, but it works...mostly, with the following notable exceptions:
-Even after formatting the hard drive with the /s switch, I had to run FDISK /MBR before it would boot from the hard drive. From what I've gathered in other posts though, this is par for the course when trying to install DOS on many newer systems.
-I cannot use EDIT or QBASIC to edit any files. Doing so causes a hard freeze whenever I try to open any of the menus. Because of this, I had to manually create AUTOEXEC.BAT and CONFIG.SYS one line at a time using ECHO commands. I must admit though, this COULD be an incompatibility with the PS/2-based KVM and/or the PS/2 to USB adapter I'm using on my workbench causing it to stop responding to keyboard input (Maybe it's getting caught up when I hit the ALT key, thinking I'm about to switch inputs?). I currently have no way to test this, as the only spare USB keyboard I have has gone AWOL.
-There is no PC speaker audio whatsoever as far as I can tell.
-HIMEM.SYS apparently cannot detect the extended memory OR has some other sort of problem that prevents it from loading. When trying to load, it shows an error message that I'm not given sufficient time to read (the CD-ROM driver clears the screen when it loads for some reason).
EDIT: Was finally able to see the error. It says "Unable to control A20 line. XMS Driver not installed."
-Attempting to use F8 to step through the startup process causes a hard freeze (another reason I can't read the error HIMEM.SYS gives), but again this could potentially be an incompatibility with my KVM and/or PS/2-USB adapter.
And now for a couple positive tidbits:
-I tested a DOS-based screen saver called Razzle Dazzle. It properly detects and runs in high-color SVGA mode perfectly!
-I discovered quite by accident that it also supports EGA mode, as that's the mode a Tetris clone I tested uses. It ran perfectly fine, minus the lack of audio.
I mostly did this out of curiosity after seeing this thread, just to see if I could do it since I had a spare Mac Mini on hand I could try it on. Beyond this simple curiosity, I honestly have no pressing desire at this time to thoroughly debug and get DOS working on a Mac Mini. 🤣