Not reading a media card limits you to using Updater.exe only. Try flashing just the Oregon 6x0's boot.bin as an RGN file. Open the O6x0 firmware in RGN_Tool and uncheck the second section. Save the file named only as OUT.rgn:
Spoiler: Image

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Flash OUT.rgn in preboot.

If it works the ramloader in virtual region 12 will be updated and device should boot to a screen showing "System Software Missing" or freeze on the logo splash screen/bootloop. We may be able to recover if any of that happens.

If nothing changes i'm out of suggestions other than to strip it for useable/saleable parts, the PCB is only good for waste if nothing can be flashed to regions.