I got it working, finally, after days of failure.
Attempted vBIOS:
First I flashed the default MSI vBIOS from techPowerup. (Smh, the whole reason I upgraded from a 780M to 880M was to get an OC without messing with the vBIOS. Oh well!)
The flash went smoothly and the Hardware ID was updated to 1198.1105 (MSI 880M). However all of the drivers still failed.
Attemped BIOS and EC Firmware update:
None of the BIOS or firmware files from MSI worked at all- for the BIOS I didn't have the install link, and for the EC FW I got "Wrong Project" error, suggesting the wrong hardware.
I ended up going to MSI Forums asking for a BIOS and FW, and paying 20 Euro to Svet (extremely helpful, completely worth it). Svet provided the correct BIOS for a Whitebook: E1763IG6.71D
The FW I updated to was 1763EG61.517
Notice these are completely different codes (1763EG6x.xxx) than the MSI official GT70 firmwares (1763EMSx.xxx).
Svet provided several tools to install these.
The BIOS update went smoothly, however the EC Firmware update gave error: Missing Myio.dll . According to Svet this was a mistake by MSI. He provided another tool to create a USB BIOS flasher loaded with the EC Firmware and this worked. Now my BIOS and EC Firmware are both updated.
THIS DID SOLVE THE PROBLEM. However, the drivers from MSI still did not work- First I tried the ones for GT70 2QD, tried again, tried the official Nvidia download from yesterday... then I got another installer from Nvidia- they had updated the drivers again (375.57, literally an update from today) and it worked. I don't know how or why, but I am now running an 880M successfully.