Did you ever find a solution to this problem? I have some ideas.

Let there be a binary decision variable for every quadruple of (player 1, player 2, showcase, round number), provided both players are in the showcase.

The coefficients of these variables in the objective function is the absolute difference in rating between the players, but if the players are in the same conference, make the coefficient extremely large, like 999999999.

Then the problem is the minimize the objective function subject to:

• the sum of the binary variables involving player i and player j is <= 1
• the sum of the binary variables involving round number k is = (number of players in showcase)/2