How broken we talkin' ?
If you can't get the screen to show any visual, going to be near impossible and probably not worth the effort. You can use the RokuTV as an extended monitor but not vice versa. (as far as I know.)
If you have visual, I guess it would be possible (maybe) to use the HDMI ARC feature and send audio out to a sound system.
My first stop for projects like this would be Youtube. Many creators always repurposing electronics to give a second life.
Roku Community Streaming Expert
Just another Roku user... I am not a Roku employee.
Insignia RokuTV, Ultra 4660x, Premiere+ 3921, Express 4k+ 3941