Line in not responding the way I had hoped

Starting off with my current setup and my expectations, I have 2 Samsung monitors that do not have speakers built in; however, they do have a audio out in the form of one mini port. So what I was hoping to do is have both monitors output the sound from HDMI through mini, into a stereo splitter, into my line in (blue audio port) on my onboard soundcard. I am having no such luck. I have a dual monitor setup where Monitor 1 is PC Monitor 1 and Xbox 360 1, while monitor 2 is PC Monitor 2 and Xbox 360 2. So my hope was that when my friend and I were playing xbox, the audio would go in from the xbox out through the mini output, and into my line in, eventually going out my optical audio port to my soundbar setup.

While I understand this is complicated, it's the only way I can really get this to work, since my sound bar will only take one source at a time, I either am the only one with sound on my xbox using optical, or we both have it by using the PC as the source.

I have updated my audio drivers to the newest (they're Realtek audio drivers), and I have everything hooked up exactly as it needs to be. I tried testing the line in with my phone to see if that would pick up any audio, and no such luck there either. I know that the monitors can control sound, because they both have audio controls on the interface, but they just don't have speakers.

If anyone could help me troubleshoot what I'm doing wrong with my sound settings, I would appreciate it. Thank you.

(Bump) Also, I have figured out recently that the line in will only output to another mini output, not a digital output. I guess this is the problem. Is there anyway to have a line in output to an optical through realtek's stupid interface? Should I get a new soundcard that doesn't use this horrid program?