Southeastern Asset Management, Dell's (DELL) biggest outside shareholder, is re-emphasizing its opposition to the $24 billion buyout of the computer maker, and now it's demanding a list of other investors so that it can take the case directly to them.

To this point, Southeastern, the holder of more than 8% of Dell's stock, hasn't been tremendously successful in getting the buyout group to see things the way it does. Southeastern was one of the early voices against the purchase, and it believes Dell is worth almost $24 a share. The takeover bid, led by company founder Michael Dell and Silver Lake Partners, is $13.65. Microsoft (MSFT) is contributing a loan.

On Wednesday, a day the 30-stock Dow Jones Industrial Average was hitting an all-time high and the Nasdaq added 1.2%, Round Rock, Texas-based Dell was gaining 9 cents to $14.09. Not exactly skyrocketing, but it is the best level the stock has seen in months and represents a post-deal announcement peak. Dell's 52-week high is $17.46. To reach that, the stock needs to climb another 24%, and in order to match Southeastern's valuation of $23.72, it would have to rise 68%. Dell hasn't traded above $20 since the latter part of 2008.

Memphis-based Southeastern sent a letter to Dell and filed a copy with the SEC repeating its unwillingness to go along with the current plan. The letter, signed by Chairman and CEO O. Mason Hawkins and two other executives, said the investment firm was unhappy with the Dell board for a "failure to implement a transaction that would maximize shareholder value and be more beneficial to all shareholders." The board, the letter contended, "has placed the interests of management above those of public shareholders."

Southeastern says Longleaf Partners Fund, its biggest client and a firm it oversees, wants the names, addresses and holdings of Dell shareholders so it can contact them about its disagreement with the acquisition proposal. Longleaf has about 30.9 million Dell shares; Michael Dell is the top share owner.

Along with Southeastern, other large resistors to the buy include T. Rowe Price and Pzena Investment Management. As of Feb. 13, holders of just under 15% of Dell's shares said they would vote against the acquisition or at least hinted that they were considering doing so.