Heya Sean. I searched the manual for your television for ARC. The manual makes no mention of ARC. I daresay if your television supported audio return over HDMI, it'd brag about the feature somewhere.
If you want your television to be an audio source through your sound bar, you ought to connect it using an
optical cable from the TV's S/PDIF output instead. That'd free you to plug your Roku into an HDMI input on your television, rather than your sound bar. I doubt that sound bar does any favors for the video output by the Roku anyway.
And if you plug your DVD player into the other HDMI input on your television, you can just always leave your sound bar on the same source all the time and use your television to switch inputs from CATV to Roku to DVD.