Thanks to several guides and suggestions I have Nintendont working on my Wii U now, using my old Wii drive, a Seagate FreeAgent 1.5TB USB 2.0... but...
Having asked the question here and elsewhere about drive compatibility, I finally read every page (yeah, that's not confusing as hell) and tried to research it on my own, and got nowhere.
The Bottom Line, I guess I have to use two drives for games, one for Wii games (a 512 byte per sector 2TB Seagate Backup Plus Desktop USB 3.0 drive chosen for space) and the old drive that I had been using - which was full - for Gamecube games, all because Nintendont can't see the 2TB drive and throws that damned DSI error on my Wii U as well. I wouldn't care except that the FreeAgent is old, and frankly I've been concerned that it's going to crap out for some time now... and it's the only drive out of the now seven drives I've tried that Nintendont will run the Gamecube games from.
Seriously?? I was lucky the 2TB was even a 512 byte/sector drive, since I haven't been able to find those new (or in most cases find anything that even says whether the drive is 512 or 4k on any website or store sales pages)...
So again, I'll ask, what's a known 2TB or better drive that is being manufactured as we speak, and currently in stock anywhere, that is CONFIRMED working with Nintendont?