The mixer you selected does not have quite the routing capabilities as the one I am using.
On my Alto, each input channel has two aux outs. There are also the stereo outputs.
I'm running the headphone output of my computer into a stereo mixer channel. That's done by using a 6.5mm male jack that is two RCA's on the other end, which I adapt to 1/4" phone plugs and go into line inputs on my mixer. I monitor that through the Stereo Left/Right Headphone jack through my headphones. Whatever I put into my stereo Left/Right mix, I hear in my headphones. That can be a live mic, a guitar, whatever. That's just the headphone mix.
For single tracks I am trying to get into the computer to record, I come out of one of my Aux outputs. That's all that is going to the computer's Line input. Most computers have a mic input. Mine has both Line-leve inputs and mic-level inputs. An Aux out is typically a line-level output. If you only have a mic-level input on your computer, then you will have to be very careful to turn down the level going into your computer's input so that it doesn't go into distortion. Having the Aux out on each channel allows me to set one level for the headphone monitoring on the mixer (left/right) and another for a dedicated output to the record input on the computer (From Aux 1 or Aux 2). Each has its own independent level for record out and monitoring.
Now you have the computer playing back sound from previously-recorded tracks, being monitored through the headphone jack on your mixer, AND you have your guitar or mic that you are presently recording ALSO being monitored through your mixer's headphone jack. You are also sending an independent output of sound to the computer to be recorded and added to its own record track.
Because your mixer has no Aux Outs, you may run into problems with having a dedicated output on your smaller mixer to go to the record input on your computer, because you don't want the playback tracks bleeding into this record track. You may have to use just the Left Side of the stereo outs for playback, and the Right side for Record output. That way you would be using your pan controls to separate the outputs. Then you would need a Stereo-to-mono headphone adapter for your headphones. Otherwise you would have an imbalanced sound in your ears. All playback in one ear, and all record in the other ear. It would probably work much better to just hear a mono headphone than to have a crazy imbalance in stereo.
I hope the way I'm explaining this to you makes sense. We're trying to work around the limitations of the input and output capabilities of your mixer.
I'm glad it makes sense to you. There really is a method to my madness.
I build lots of crazy-loop contraptions to get myself where I want to go. Surprisingly, just about everything I cook up like this seems to work just the way I thought it would.
As information to all the Behringer Xenyx Q502 USB Mixer DID NOT WORK OUT for Johan.
He needed a mixer with Pre-fader Aux sends on each input channel.
He ended up sending it back and got a mixer that was more suitable for his purposes.
He is now happily tweeking the knobs on the Behringer Xenix X1222 USB which cost a little more, but is more of a dream-come-true than his original choice.
Fortunately, the dealer gave him full credit on his exchange for a better mixer.