I'm trying to amplify the headphones output of my laptop as the volume is too low during calls and such. The laptop has a combined TRRS female 3.5 jack output. I've used a splitter to split that into separate headphones and mic TRS, then using a reverse splitter I've connected the microphone directly and diverted the headphones to an amplifier (see picture).
The setup works correctly without the amplifier (ie if I connect the two inputs to the two outputs). Also, with the amplifier in the mix, the mic works fine. The issue is that when I connect the amplifier I can't hear anything from the headphones. Connecting normal headphones with a TRS jack to the amp output I can hear stereo sound and at the same time use the mic from the headset, it's just that the headset doesn't seem to receive sound when connected to the whole setup.
What am I doing wrong? Each component works well individually, so I've (perhaps prematurely) excluded a channels crossing problem...