Recommendation for stereo speakers that will be several feet from nearest wall

Options
I want to put a pair of speakers in the living room part of an open plan home with a cathedral ceiling, and the only feasible place from a design standpoint is in front of the stairway that leads downstairs. The stairway is open, i.e. a series of oak posts six inches apart keeps you from falling in (banister with balusters). The net is that the speakers will be about four feet from the "back wall". I'm not sure that ported speakers are going to do much good in this situation.

This is not my primary listening room, but it would be nice to be able to listen to music on a decent stereo before, during and after dinner, particularly for those sitting in the "living room" waiting for me to finish cooking.

I've got a Yamaha Aventage RX-A2030 (older beast, plenty of power) directly below in what is my primary AV room. The plan is to make the upstairs a "zone 2".

The other design considerations are that (1) bookshelf speakers are preferred; and (2) walnut/cherry finish is preferred. Any recommendations in the Polk line? I've used and enjoyed Polk bookshelf speakers in the past.

TIA.