Question / Help Dual PC Audio Setup

[Sartic]

I'm currently looking at getting a mixer, but before I do, I want to make sure I have everything set up properly so I can buy all the wires I'll need in advance. Here is the setup that I've come up with:

If anyone that has some experience with audio could tell me if I'm setting this up right, that would help out a lot. If you think that there is a better way, please give me suggestions :)