My bricked unit is still spitting jibberish out the console serial port regardless of the method attempted.
I’m afraid you can’t boot SBC from uSD because internal emmmc flash is used. Per:
https://www.digi.com/resources/documentation/Digidocs/90001531/#reference/6ul_sbc/r_boot_mode.htm?Highlight=j10
By default, the ConnectCore 6UL module boots from the internal board settings, allowing it to boot from internal NAND memory. However, it is possible to boot from USB through.
So recovery in case of cc6ulsbc is done via USB:
https://www.digi.com/resources/documentation/digidocs/90001515/default.htm#task/yocto/t_faq_recover_device_yocto.htm%3FTocPath%3DDigi%2520Embedded%2520Yocto|FAQ|_____1
Why do you want to boot from uSD?