Your computer speakers have 3 built-in amplifiers. They have a line-level stereo input that might look like a headphones jack.
Your stereo receiver must have a stereo line level output to feed a recorder but it can feed the line level input on your computer speakers.
I have no dea why you shorted things with a "bypassing speaker signal splitter". The outputs of amplifiers MUST NEVER be shorted together.
You need a shielded audio cable that has a plug (not a jack) that matches the line-level output jack on your receiver on one end and a plug that matches the line-level input jack on your computer speakers on the other end. The amplifier outputs connect to the speakers, not to the line-level signals.
The stereo receiver feeds its own speakers and the computer speaker amplifiers feed the computer speakers. They should be "in sync" but might be out-of-phase.