INVESTMENT FIRMS HAVE 7.7 PCT OF MIDWAY <MDWY.O> Two affiliated investment firms told the Securities and Exchange Commission they have acquired 593,000 shares of Midway Airlines Inc, or 7.7 pct of the total outstanding common stock. The firms, Boston-based FMR Corp and Fidelity International Ltd, a Bermuda-based investment advisory firm, said they bought the stake "to acquire an equity interest in the company in pursuit of specified investment objectives...." The firms said they may increase or decrease their stake in the company, but have no plans to seek control of the company or representation on its board.