Sony Group Agrees in Principle to Buy MGM  PHILADELPHIA (Reuters) - A group headed by Sony Corp.  &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=6758.T target=/stocks/quickinfo/fullquote"&gt;6758.T&lt;/A&gt; agreed in principle to buy 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 nearly \$5 billion on Monday,  sources close to the deal said.