I used the above diagram to wire up my USB Dac and it's working but the volume dial only works when headphones are plugged in. The speaker does work when phones are unplugged but there is no volume control. Any thoughts?

I just got a pair of XIANJIE 3.5 Composite Displays. The seem to work great. The price was $28 each plus shipping. The website used to order is a bit odd, but that's the only down side so far.