9200 shouldn't be a problem alright.
Is port 9200 open in your router and pointing to your Diskstation?
A simple way to check to see if it's done and working is:
Close to the bottom of the page under the google advertisement you'll see the results of this check. Either successful or red to say it's not forwarded.
Some ISP's block port numbers cause they hate you and want to make life difficult. (Synology did a webinar on it ->http://www.youtube.com/watch?v=W0R1ZO7r-CQ&t=3m24s
Go to http://portforward.com/
. let me know how you get on.