A:Answer I expect the result to be pretty lousy, to be honest. As even if you set the receiver to extended stereo/mono and send the full signal to the polk, it won't be like a soundbar, or even the cheapest bookshelf speakers. It'll simply be one speaker in mono.
No stereo sound. At least soundbars do the stereo thing, albeit with small drivers close to one another.
You'd be better off first buying bookshelf speakers, run them in stereo + sub, no center. Then add a center later.