Solved! Trouble setting up passive speakers and active subwoofer with PC

[HailHorrorHail]

I have very little experience here and have basically just been plugging things around. I thought I'd finally figured it out, but now my subwoofer is working and my left bookshelf speaker is working, but the right one is extremely quiet. All of the equipment involved here has been tested on its own so I know none of it is faulty.

Here's how I'm set up currently:

3.5mm splitter into PC audio jack, in one side of the splitter is a 3.5mm to RCA, the red end of which is run into my SMSL SA-50 amp. The white end is run into my Mirage Omni S-10 powered subwoofer. In the other side of the splitter coming from my PC's 3.5mm jack is another 3.5mm to RCA splitter, this one is running to my amp's other RCA input, there's one for left and right. My Event 20/20 passive speakers are both run into my SMSL SA-50's speaker posts.

I'm hoping I'm doing something really obvious here that will give you all a laugh and is a simple fix. If anyone could tell me how to configure everything so that it all works please let me know. Thanks!

For reference, the amp has a right and left RCA input and right and left speaker posts, the sub has right and left speakers posts and a single sub out RCA port.

 

[hang-the-9]

Sounds like something in the splitters you are using is causing the signal drop to the speaker. If you swap around the connections does the right speaker become quiet? Or you are sending only one side of the stereo signal through all those splitters with how you have them wired. You may also want to check your sound card options to see if it can be set to sub out. Or get a amp with a passive sub out on it.