Making the connection from my desktop computer to the remote XIS server required three steps. Determining the steps required the help of the Sonic support team and took a non-trivial amount of time so let me document them here.

1. Set the com.exln.dxe.iorport property in the [XIS_HOME]/config/xlnserver.properties file. Mine is set to 1052. Note that actual port number that you pick is unimportant as long as it is between com.exln.dxe.minorbport (1051 by default) and com.exln.dxe.maxorbport (1055 by default).
2. In the same file, set the com.exln.dxe.host property to the fully qualified host name or the IP address of the XIS server or cluster.
3. Use the following code as a template for your own connections in your client code. Make sure that the IORPORT number that you use is the same as that in the xlnserver.properties file.

   		Properties p = new Properties();
   		p.setProperty("com.exln.dxe.adminhost", [IP_ADDRESS_OF_XIS_SERVER]);
   		p.setProperty("com.exln.dxe.adminport", "1050");
   		p.setProperty("com.exln.dxe.iorport", "[IORPORT_NUMBER");
   		try {
   			this.session = XlnClientSessionFactory.getSession(p);
   			if (this.session == null) {
   				LogConfiguration.message("UNABLE_TO_GET_CLIENT_XIS_SESSION");
   			}
   		} catch (Exception e) {
   			LogConfiguration.message(e, "UNABLE_TO_GET_CLIENT_XIS_SESSION");
   		}