Updated from 8 a.m.

VNU agreed to sell itself to a private equity consortium, but two big shareholders -- one of whom has demanded a breakup of the Dutch media company -- are threatening to hold out.

AlpInvest Partners, Blackstone, Carlyle, Hellman & Friedman, KKR and Thomas H. Lee said Wednesday they would pay roughly $9 billion for VNU, whose assets include Nielsen Media Research and Billboard magazine. The purchase price represents a multiple of 13.4 times earnings before interest, taxes, depreciation and amortization. The buyers will keep VNU "substantially together," they say in a press release.

"Based on a long and careful analysis of various alternatives, including remaining a stand-alone company and breaking up the company, we concluded that this transaction best serves the interests of VNU's shareholders, clients and employees," said Aad Jacobs, chairman of VNU's supervisory board. "The all-cash offer provides shareholders with an attractive price that fully reflects the independently assessed fair value of the company."

But not everyone was so smitten with the deal, which is worth $10.3 billion including debt assumption.

Fidelity International, which owns 15% of VNU, and 2% holder Knight Vinke Asset Management say they want more money. Their possible opposition is important because VNU holders must tender 95% of outstanding common and preferred equity for the deal to close. Knight Vinke and VNU have clashed before over the Haarlem, Netherlands-based company's plans.

"Knight Vinke Asset Management believes the private equity consortium offer for VNU of EUR28.75 per share, announced today, substantially undervalues the company," the money manager said Wednesday. "Fidelity International is unlikely to support this offer," said Richard Miles, a spokesman for Fidelity International.

Knight Vinke said it believes that the board should be open to a public sale process, which could include a sale or spinoff of VNU's Media Measurement & Information and Business Information divisions.

A representative for the private equity buyers declined to comment.

Last year, Knight Vinke successfully thwarted VNU from completing a deal with IMS Health ( RX).

On Dec. 14, VNU said that it had received interest from various parties for its assets. In mid-January, a consortium of seven private equity firms emerged as bidders for the media company. Permira Advisors later withdrew from the group.

Early last month, reports said Knight Vinke had tried to stop the company's plans to be acquired by the consortium.

In a Feb. 16 proposal to the board, Knight Vinke said VNU should "solicit indications of interest from potential acquirers of the main constituent parts of VNU including AC Nielsen and Nielsen Media Research businesses (separately) and give equal consideration to a wider range of alternatives."