From the product pages it's not clear if this configuration is possible WITHOUT a Streambar:
Roku Wireless Speakers (front)
Roku Wireless Speakers (surround)
Roku Wireless Subwoofer
This would essentially be a 4.1 configuration.
I have the Roku Soundbar, and I don't care for the built in streaming capability. It causes confusion in my household, as sometimes people accidentally switch inputs to the Soundbar and don't understand what's going on. It also uses one of the TV inputs, of course. If we can build a full surround setup without it, that would be nice.