Tribune Co. is inviting at least three potential buyers who each submitted bids for the Cubs and Wrigley Field near or above $1 billion to participate in a second round of proposals, according to a person involved in the process, as reported by ESPN.com on Thursday. Several bidders offering between $700M and $900M have been excluded from the second round, according to the person, who spoke on condition of anonymity. Included in the second round are NBA owner Mark Cuban, the Ricketts family, and a group led by Sports Acquisition Holding Corp. that includes Henry Aaron and former Republican Congressman Jack Kemp.