So I reformatted the 3 TB into 3 separate 1 TB drives, and it still won't recognize any of the drives.
Is your drive port-powered or externally powered? The Roku's USB port may not be able to supply enough power to power your drive if it is port-powered. Quoting Roku's support, "USB flash drives and externally powered USB hard drives work best with the Roku player. Some USB powered hard drives will not be able to draw enough power from the Roku player to function properly, especially if used with another drive on a USB hub."