We had the Yamaha rep in our store when this first came out and set it up for us on the fly, it sounded.....ok. I'd say it gave the effect of surround sound better than other one-speaker solutions (Polk soundbridge). Since it has more drivers that can help. I never understood how Polk said they could do it passively with only nine drivers. But yes, the room does have to be pretty small and rectangular (as our demo theater was). The sound didn't reach all the way behind you, more like just to the side of you, you could definitely tell it wasn't surround sound for real, but if you want the effect and don't want rear speakers, I'd give it a shot (and your room dimensions were fitting).
the Yamaha rep also told us that you could listen to two things at once, he used the example of side-by-side picture-in-picture, and said the YSP-1 could play one source out of one side and the other out of the other side, the center speakers would act to cancel out the sound from the opposite side so you didn't hear it. I don't know if it actually does this or not or how well it works since we never had it set up after he brought it in. Hope that helps some. Oh yea, and the YSP-1 does have a sub out on it so you can hook a sub in.