Hello Dwight,
Congratulations on the Super 3XRS's. Great choice, and your other gear looks pretty nice too.
I have the same speakers as you and drive them with a couple of watts of SET power and have no need for a sub, not to mention the imaging is insane.
Play around before buying a sub. I personally like to keep things as minimal as possible in my systems, and it has paid off handsomely in sound quality and purity.