Safari problem with M-AUDIO digital interface

I have an M-AUDIO DUO device into which I have plugged a guitar and a microphone. I wish to send the USB output over the internet from my Safari browser using a URL provided by a teacher who is using eCAMM. When I launch the eCAMM URL, I get to choose which device I wish to use for video (I use the FaceTime HD Camera in my iMAC) and for audio. As I wish to send the guitar signal AND the signal from my microphone, I select "USB AUDIO CODEC" rather than the default "iMAC Microphone". (This is what is used by the M-AUDIO digital interface).

Problem: Safari is only sending signals from one of the two devices plugged into the M-AUDIO box and not both. (It sends the signal from the device plugged into input 1 and ignores input 2). I tried a whole lot of things including creating an "Aggregate Device" in the MIDI set up but no joy.

Solution: I ran the same URL on a CHROME browser on the same iMAC, making the same selections as I did with Safari for audio and video devices. All good with CHROME - it sends both the guitar signal AND the microphone signal from the M-AUDIO box.

What do I need to change in order to get Safari to do the same as Chrome? I am totally stumped but glad I eventually found a solution.