Managing multiple audio sources

I'm struggling with managing multiple audio sources using Ubuntu-Mate 64bit 20.10 on my RPi4.

I have an external USB Audio Codec device (Signalink) connected to support my Ham Radio setup so I can use the JS8Call application to Tx/Rx digital modes on my transceiver. I have the JS8CAll application configured to use the Signalink device and it works well. The device shows up on the Sound-Hardware as PCM2906C Audio CODEC but in the JS8Call application I end up selecting:

I also want to be able to play music through the Headphone jack on the RPi4 while simultaneously running the JS8Call app. The Sound-Hardware shows the Headphone jack as Built-in Audio (twice for some reason). can I associate the different apps to the appropriate hardware, and be able to control the volume individually?