getting new Mixer: Mackie???

[Monolithent]

The ports on top seem to be a match to the main outs on the back from what I can tell from the schematics.

And your wife will be unhappy to know that the knob for USB input is the only way to control the input level of the USB section. That particular input is routed to the main bus and then the output sliders. Most mixer manufacturers don't take karaoke seriously and don't intend for us to be using their gear for our purposes. The USB inputs on most mixers are either for studio mixing setups or when a band decides to take a set break and want music to play for the crowd.