Nexus 6, Deleted System Partition- Cannot Recover

The system partition was deleted and the phone has TWRP. The mac recognizes the ADB device and the MTP. Tried toggling the MTP, no success. Currently android file transfer fails every time due to a missing MD5 file in the android 6.0.1 zip, although all that is being attempted is a drag and drop. ADB sideload says it has completed but no files appear on the phone to flash, or in the file explorer, and so does ADB push. Tried re-downloading the rom, rebooting the phone and everything else.

Any help is appreciated.

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