Edgar Bronfman Jr. is trying to put together a group to buy back many of the entertainment properties his family sold to Vivendi in a deal that turned sour, according to several executives close to the negotiations. Among those mulling whether to join Mr. Bronfman in bidding for the Vivendi Universal assets, these people said, are Cablevision Systems, one of the nation's largest cable operators, and several private equity firms, including Quadrangle, led by Steven Rattner, a member of the Cablevision board. Among the other private equity firms that Mr. Bronfman has approached, the executives said, are Providence Equity; Kohlberg Kravis Roberts; and the Blackstone Group, which is said to be interested in acquiring the half-stake in Universal's theme parks that it does not already own.