Would I be able to put 2 of these same cards in 2 pcie slots and configure them to function together as 8x8 mu-mimo? Assigning one card working as 4x4 input and other as 4x4 output, therefore increasing and easing up channel space.
Is there a software or a feature in openwrt to do this?
afaik MIMO is done by the card's hardware as it requires low-level radio and antenna information.
The best you can do is to create two wifi networks with the same name/password, and put directional antennas so each wifi network will be mostly covering one zone, this will let the devices choose the one that has better reception