I'm in a similar situation as yours, since you have an AVR you should be looking into a 'passive soundbar', basically it's just 3 set of speakers in a soundbar form, each speaker, L/C/R is divided with its own chamber, check this thread for a pretty good list of passive soundbars: http://www.avsforum.com/avs-vb/showthread.php?t=1285715
Price range varies from 500-above 2k, so check those out and see which fits your budget/size/look.
I'm debating between a few within that post myself, goodluck with yours!
I have an open space similar to this. I normally do not really turn up my soundbar too much, but when I do turn it up I get some real good sound from mine and the bass is good from the sub which sits right next to me.