Just use a HDMI splitter instead, one output to your display, the other to your capture card.
Edit: ok I think I misunderstood your problem initially.
Actually, it should be no problem to get audio out of the AV1/2 3.5 mm jack, simultaneously with hdmi audio output. Make sure the switch is set to AV1 out, instead of AV2 in.
This reply was modified 7 months, 2 weeks ago by Harrumph.