Use PLOP boot manager:
https://www.plop.at/en/bootmanager/intro.html

Install it to a floppy, boot from floppy and then select CD-ROM. It will then proceed to boot from CD.

I've tried to use the plopbtrom.bin as an extension ROM(using plopcfgbtGUI.exe to configure it, saving it using the button at the bottom right(Config...(something), as far as I remember). Then I tried loading it in UniPCemu together with the AT XT-IDE BIOS and VGA BIOS), but the Compaq Deskpro 386 BIOS doesn't even try to use it? It simply continues normal booting through the XT-IDE BIOS.

Am I doing something wrong?

Edit: Managed to get it loading using the plpbtrom executable.

Edit: No menu appears(just a raster). Pressing c to boot from cd-rom raises a general protection fault, with 1xa234 being displayed in the top-left corner of the raster/screen?

After the latest improvements and bugfixes, it doesn't display any menu, but shows 1xa in the top left corner of the raster background after pressing the c key while it's showing?

Edit: I also see it's scanning the reserved memory area at F00000-FFFFFF(Moving zeroed EAX DWORDs there), using FS:EDI?

Edit: It eventually hangs itself up with a HLT instruction at 2000:13BC(real mode)?

It now displays the code 1xa234? That looks like some debugging address for checking memory accesses? Or is it... ?

I've found a bug in the 32-bit modr/m processing(truncating all 32-bit offsets to 16-bit). With this being fixed, now memory past 1MB is addressed correctly and the boot manager shows two things: a SHUTDOWN option(which, when entered, starts booting disk A(I think, although the Compaq BIOS will hang due to invalid DMA controller programming(being in test mode instead of read mode)) and the system time counting in the lower right. 😁 Although no other options are displayed, besides the SHUTDOWN option(maybe they just aren't visible)?