I am looking to connect multiple audio sources (laptop, tv, echo, etc.) which use aux outputs (and have them play simultaneously) to a single 2.1 channel multimedia speaker system which uses a TRS 3.5 mm input. I tried using a mini soundmixer and while it allows the multiple sources to play audio simultaneously, the sound only comes from one of the speakers, not both. I tried using a y cable to break the aux into left and right and have the mixer mix those into one.
tl;dr trying to connect multiple audio sources playing at the same time with trs outputs to a 2.1 channel speaker set.
Sounds like the mixer is single-channel not stereo, if that is the case you would need to have L and R as separate inputs (e.g. channel 1 for L and channel 2 for R) and use the pair as a source or target but that may not work if the output is also mono on the mixer.