I think the Roku wireless speakers will only pair with Roku TVs. @Tivoburkee probably knows more than me. Roku software version 11.5 supposedly allows you to pair Bluetooth headphones to an Ultra, so I assume a Bluetooth speaker would pair as well. My Ultra (4800) hasn't received 11.5 yet, so I can't test it.
Roku Community Streaming Expert
Help others find this answer and click "Accept as Solution." If you appreciate my answer, maybe give me a Kudo.