text: XM Satellite Up, Sirius Down Before Bell  NEW YORK (Reuters) - XM Satellite Radio Holdings Inc.  &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=XMSR.O target=/stocks/quickinfo/fullquote"&gt;XMSR.O&lt;/A&gt; shares rose nearly 6 percent before the bell on  Wednesday ahead of a news conference the company is holding in  conjunction with Major League Baseball.