Well, you MUST get a subwoofer with that Polk 5.0. Those little satellites produce absolutely no bass. They only go down to about 130hz. The only have a 2.5" driver/woofer.
You can do without a sub with the Jamo tower setup. You'll want one in the long run but at least you can listen to movies and music without it.
I would get the Jamos in a heartbeat over the Polk RM75.
And yes you are comparing apples to oranges.