ACC champ is in for sure (either Clemson or Miami)
SEC champ is in for sure (either Auburn or UGA)

Scenario 1:
Wisonsin wins = they are in
OU wins = they are in

Scenario 2:
OU wins = they are in
Wisconsin loses = toss up between Bama and OSU, would make for some lively debate

Scenario 3:
Wisconsin wins = they are in
OU loses = Bama is in, not much debate here imo

Scenario 4:
Wisconsin and OU lose = Bama and OSU are both in.

I really don't see any scenario where somebody other than those six makes it in though.