Do omnis present challenges for room treatment, or do they solve some of it by radiating in all directions?
The Ohm's aren't "true" omnis, and this is by design. The "CLS" drivers deliberatly attenuate output in the rear in order to avoid rear-wall reflections that can confuse imaging and otherwise muddy the sound. One nice byproduct of this is that they don't have to be way, way out into the room, an obvious plus in a room of your size. Also, because they are very easy to move around (no spikes!!!) it's very easy to experiment with positioning, and/or to move them into position when you are listening and out of the way when you're not.
There's no way to know what a given speaker will sound like in your room until you set it up in your room with your associated equipment. Again, with the 120-day Ohm home audition, you can do this with no risk except for the cost of return shipping.