Greetings from the Roku Community, @Chinna!
It is highly appreciated that you've reached out to us for support and we'd be more than happy to be of assistance here.
Before we proceed, may we first know the model of the TV your surround speakers are connected to? We suggest directly connecting your Roku Ultra to your TV rather than to your Sony STR-DH790 Receiver.
Furthermore, kindly visit our Support article on How to set your Roku streaming device to another sound system.
Please keep us posted on how it goes and we'll continue assisting you from there. We'll be looking forward to your update!
Best regards,
Carly
Carly Y.
Roku Community Moderator