thanks Newman.

I just received this from TD Ameritrade client services which may be useful,

Purchases of XMSR prior to the merger would not be considered "substantially similar" because the two stocks were still separate companies. Securities are considered substantially similar if they can be converted to the sold security at the holders request. Examples of substantially similar securities include call options, warrants/rights, or convertible bonds for the security sold at a loss. Since the merger was decided by the companies, and you did not have the choice to elect for conversion, XMSR was not considered substantially similar. This being said, the purchases of XMSR were converted into the SIRI history in GainsKeeper, and may trigger future wash sales if you sell the converted shares for a loss, and repurchase shares of SIRI within the wash sale window."