My recommendation would be the new Sonos AMP with a pair of in-wall speakers and Sonos sub.

I've been a beta tester for the Sonos AMP, so have had one at home for 3-4 months and have been really impressed with it.

If you don't want to upgrade the TV right now for ARC, you can connect the Sonos AMP to your existing TV using an inexpensive HDMI > digital optical converter that would connect the AMP to your TV the same way you're connecting the existing Playbar.

Operation would be the same as what you have now, but you'd have much better audio quality with the AMP/inwall speakers + Sonos sub.