It does sound like a firmware issue. Are the partition tables on the CF cards different? I also wonder why it won't boot from USB. All mainstream Linux distros can install in either BIOS or UEFI mode. In fact if you want to use UEFI it is best to disable BIOS in the firmware.
DistroAstro is just Mint with a lot of software (or varying quality) pre-installed and a night vision mode. The Mint build used for Astro is a bit out of date and I doubt Astro is as well maintained as Mint. So I've opted for Mint and I'll install whatever software I need. Of course I'm not interested in the night vision mode, but you possibly are. I've attach a list of all the software that is on Astro that interested me but isn't in the Mint repositories. I wouldn't worry about elementaryOS just yet.
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