3.5mm jack mixer

[HexTank]

I'm about to make a bartop cab but am wanting to have an audio mixer, as I'll be using an original XBox as the controller, having audio playing along side is limited so I though of adding a jack in to the mix.

I've looked at the small amps people tend to use but none appear to have any mixing between inputs (unless somone knows of one) so I guess the only alternative is to wire up my own passive mixer and route that to an amp, I'm guessing I just would need to put something like a 1kohm resister in series with the live wires for each stereo signal.

Does this seem reasonable, or better yet, does anyone know of an existing amp with build in mixer (there's the karoeke ones but I'm looking for stereo + stereo, although that might not be an issue give how close speaker will be to each other in the cab)

Cheers.