Actually, the room causes a gain in low end, so the -9 is still supposed to be usable in room.
You should always leave the receiver set to it's highest (usually 8, but on some 6 Ohm) setting regardless of the speaker used. The lower setting is for a UL rating, and only causes the amp to have it's current limited, which is not a good thing.
Some midrange drivers start to break-up (non-uniform cone movements that cause distortion) at higher frequencies, so sometimes a lower crossover point is better. At the same time the lower point will place more load on the tweeter. Like most things in speaker design, there are trade offs. All of this is completely dependent on the driver selection, and thus up to the designer where to best place the point.
