How do I run laptop headphone out through my Scarlet 18i20?

Hello, I'm not sure what to call this post, and I apologize if this is a dumb question.  I have tried a couple times but never seem to get proper results.
 
I currently have a Scarlett 18i20 that is connected to my desktop computer via usb.
 
I want to be able to use my laptop to listen to music on the Cakewalk Songs Forum through my studio monitors.
 
I tried to take my headphone out on the laptop and run it through 2 new inputs of the Scarlett, but I get no volume.  The monitor volume has no influence on the output.
 
Has anyone ever tried to do this and had good results?  If so, what was your procedure for getting it to work correctly?
 
Thanks in advance.
 
jqs

fireberd
If the Scarlett is set as the default Playback device in Windows then you don't need to connect a headphone/line out to the Scarlett.  It should playback whatever audio the PC outputs.  

Hello firebred, thanks for your reply.  I might not have been clear enough, so accept my apologies for that.
 
Yes, I understand what you are saying, but that would mean I would have to unplug the USB cord from the back of the desktop computer, and plug it in to the laptop.  That would most certainly work. 
 
I am trying to avoid having to do that.  I would like to have the main desktop plugged in via USB, and still be able to listen to music from the internet, through my laptop, to my monitors.
 
Of course, the easy way would be to just allow my main desktop to be internet enabled, but I am trying to avoid that, (for various reason, valid or not.)
 
I hope that makes sense.
 
Thanks for your help, if you have other suggestions please let me know!
 
jqs
 
 

azslow3
That should work in case the cable it correct (most modern notebooks have 4 pin audio connector for headset and at least once I had 3 pin connection with somehow unusual pin sizes...).
Check Focusrite Control for routing: https://support.focusrite.com/hc/en-gb/articles/115004431669-Focusrite-Control-Tutorial-I-Understanding-Focusrite-Control , "Custom Mix" section.

Thanks!  I will give that  a try.

Alright, thanks Jeff, and azlow, and firebred, all valuable insights to build my knowledge base.
 
But let me come clean a bit.  I have it working now, In reality, this was a situation where I was not thinking critically, I asked the question before I really dissected the problem.
 
Granted, sound from one device to another is always predicated on proper routing, that did not occur to me at first, and therein lie my disconnect.
 
Once I realized that I had to have a program that provided a choice of inputs, such as Sonar, I was able to route the headphone Jack through the Scarlett, through tracks 1 and 2 of the daw, to the main outs, and I was good to go.
 
That begs the question. whether this is the way to reach the highest playback fidelity, or not?
 
So I will look at other routing options, hdmi, digital, so on, and see if I can improve.
 
As an aside, now I have a new issue; every time I open Scarlett Mix Control, I get an error message saying I need to upgrade the firmware.
 
Oh well, at least I can listen to the Song Forum on my Macks as opposed to my AKGs.
 
Thanks Doots
 
jqs