So I accidently had the 50k and 100k pots in the wrong places. I updated the schematic above. Things are now as they should be.

A rough estimate of the cutoff frequencies can be found with  F=1/2πRC
F= Frequency
R= Resistance in Ohms Ω
C is Capacitance in Farads.

The bass control with control the volume for everything below 482Hz. The Treble control will control the volume of everything above 568Hz. Both filters have a -6db/oct slope.  There might be some slight mid range scoop in between those frequencies,

One question before I start, around what Hz will the .01uF caps be affecting?

If it truly has 39k Ω of resistance than that means it's maximum possible resistance will be 39K. If the slider is set to the middle, than both sides only get half of that total. I'm not exactly sure 39k Ω will be enough to silence the unwanted track. If it ends up being too little resistance you can always try this configuration instead.

if all else fails, make two seperate volume knobs and crossfade it live

so... the 039k on the fader what does that mean? resistance on both channels in the middle or just one when its over to the side?

Sure thing! Let me know how it works out.

Hey, thanks for sharing those Tyler. Gonna try the second one out!

It also depends on how complex you are wanting to get. Here's a couple ideas I came up with for a completely passive mixer with tone controls.
Just determine whether you want your volume controls independent or just one master volume, and whether tone controls are worth it to you.

EDIT: I had to update an error in schematic.

I guess the most obvious solution would be this.

this is what it looks like soldered in to a small radioshack project board.

Help me to design a passive mixer with a cross fader. I fried a djx2b trying to circuit bend it, and harvested a lot of neat parts. the cross fader has 039k stamped on the side of the chassis.