OK - I wasn't sure about the headphone output on the LG.

So with that information it's a pretty easy solution.

I would probably opt for the Mackie mixer since it already has a 3.5 mm input. A simple 3.5mm cable should be all you need to connect from the LG to the Mackie.

Like this

https://www.amazon.com/Syncwire-Braided-Auxiliary-Adapter-Headphones/dp/B01I0SI1SG

You might have to turn the volume way down on the LG TV because the headphone output signal used to drive headphones is a bit strong for the line level input the Mackie mixer is expecting. But other than that it should work fine.

For the Mackie mixer main outputs to the Rockville input connection you would need a dual mono 1/4" to RCA cable like this https://smile.amazon.com/Cable-Adapter-Stereo-Interconnect-Quarter/dp/B08TT82L1T