I had mine in a 13x17 room, with a 8.5 foot ceiling. I may be in the minority here, but my only real concern would be that sloping ceiling and where your speakers are placed vs where you sit. You have limited options I am sure. A great bookshelf design and a sub may give you more flexibility. Or, a great powered bookshelf might be even better.
While they play very low and accurate, the SS8 isn't a "thumper" in the bass range. Bass is harder to dial in than mids and treble, and that smaller room might complicate it. You may have to place those speakers a bit closer to the wall than optimal, but you won't be dealing with ports. Placing them closer to the rear and corners may lead to a bit of an increased and possibly more boomy bass response, but you might find that you like that.
Some pro's in the case of the SS8 for your application would be that is is not a ported design. You can also play with the rear baffle to dial in the mids and highs.
You could also talk to jim about the SS7 either in a floorstanding or stand mounted design and get a smaller sub that you could blend with the mains and give you a little more in the way of placement options.
Or, possibly get one of Jim's new powered speaker designs, save some space in your rack in the process. I've not heard Jim's powered speakers yet, but I've demo'd the DynAudio Focus XD series and came away incredibly impressed at the quality and output of the entire line-up. It was likely the most impressive bookshelf I've heard (XD200). Even the bass hit low and accurate.