Sony Group Agrees in Principle to Buy MGM  PHILADELPHIA (Reuters) - A group headed by Sony Corp of  America agreed in principle to acquire Hollywood film studio  Metro-Goldwyn-Mayer &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=MGM.N target=/stocks/quickinfo/fullquote"&gt;MGM.N&lt;/A&gt; for \$12 a share in cash, MGM said  on Monday.