I'm not too savvy on sound stuff but I had to get a soundbar as my new tv's speakers were rubbish. I connected it to the TV, then the sound from everything else that is also connected to the TV comes thru the soundbar.
If your TV has an Optical input just connect the soundbar to that. If it doesn't you'll have to use the other method.. can't recall name but it's the headphone socket thingy. . it's the one I use so I can use my tivo remote to control the Tv volume and mute button as it doen't work with my soundbar
Sorry not that much help, am sure some more techy person will come on and make more sense .
By far the best way, if your soundbar has the capability, is to take the hdmi out the tivo into the soundbar, and out of the soundbar into the tv. You'll avoid a lot of issues with the optical audio out interface on the TiVo. Also if you're lucky then doing it this way you might benefit from CEC between the soundbar and the TV (ie. TV and soundbar switch on and off in sync rather than independently.)