this answer went a bit over my head.
not sure if you could go into more detail?
I have the kona Lh card...so i follow what you are
saying about the first 2 outputs going to kona but
not the 3-4 alt.
The mixers main outputs would go to your audio monitors, and your main level would be the master volume for all channels. The mixer's Alt 3-4 outputs would go to your cards analog audio in, or to a patchbay with a set of inputs connected to the Kona's analog in, if need be....which would be a good idea if you needed to patch another line-level audio directly to the Kona in for a direct audio capture, bypassing the mixer.
On each input channel, the mute buttons also route that channel to the Alt 3-4, effectively cutting the signal going to main so you won't get feedback from the audio monitors when using a mic, routing the audio directly to your computer. And you can adjust the alt 3-4 out level with a separate master dial.
I agree with Yoink about exercising caution when buying used. These can be rugged mixers, but they are also used on the road a lot...knocked around sometimes or what have you....constantly plugged in and out. Normal wear and tear, really. But they are so affordable that you might as well buy new and get the benefits of return policy/factory warranty if something does go wrong.
If you do get one, and you need help connecting it up, shoot me an email and I'll help you out. Good luck.