Not sure if y’all are new to mining but undervolting is not considered crippling the card in mining when you have power usuage to consider. Also, are you sure 300 watts on each 1080ti is accurate, nor,ally it’s like, 180 to 200 watts.
Finally, I’ve never seen a build where a card with 2 connectors on top weren’t run off a single pcie using a splitter from pcie to two 6+2 plug, that’s how all 46 of my 1070ti are wired, of course I’m not running at 300watts a card.

In the reddit post about octomimer mobo, they guy from company posted a link to the 1080ti models they were testing 8 of and he was supposed to temperature results. I know he said since the board uses mobile cpu and ram, it only draw like 40 watts so almost all your 2200 watts is available for cards. Hope that helps