Hi Mark, have you tried enabling Advanced TX mode and setting the input device to your headset?

Mine looks like this with my Sennheiser headset. I use a footswitch on transmit, wired into the RJ45, but you can enable VOX or use the PTT button on the Advanced TX panel.  I just sang myself a few notes into the Mow Cop WebSDR on 10 GHz, 150 km away over the Pennines, using the DUO as the IF driver for my 10 GHz transverter and it worked fine. 

It also works if you pipe the audio stream via a Virtual Audio Cable instead of using the headset mic device and pick the VAC as the audio in device.  Can't say I ever do it this way in live use because I prefer my Heil Pro7, which plugs into the RJ45 and the headphone jack.

Neil
http://g4dbn.uk