The onn roku soundbar uses the same IR commands that roku's 12 years ago used, so yes for sure it will control the actual roku commands. The Onn's tv controls are roku cec commands, so if the universal remote doesn't have those, it won't matter because your tv volume should control the soundbars volume, so as long as it has a code for your brand of tv it should all work. Just have the tv volume punched through to roku device on the universal remote.
Edmund
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