Duke would be an AWESOME get for the Big Xii! FWIW, I've been to a football game @ Duke, and it is a cool old stadium that actually hosted the 1942 Rose Bowl.Duke has a huge national brand, massively respected global university. Even though their FB kinda bites, the others aren't Alabama either - you have to take Duke in that instance. Then pick one of GT, VT, and LV - don't care much there. Weight out the tv markets, alumni base et al and pick the best fit.
Second thought, just take ALL what you have listed and go to 24. 3 protected rivalries, and play 5 of the other 20 - so you'd cycle thru the league in 4 years time. Or do old school, three 8 team divisions, take the champs and a wildcard for a conference playoff.