[Jackaudio] How to play MIDI sounds through Zoom conferencing?

Hello, all, newbie here, both to this forum and to music. I'm a first year music theory student at my local community college. I'm searching for a definitive answer to the question, How to play sounds from a MIDI controller to the other participants in a Zoom video-conference? I've successfully hooked up my Korg microKEY controller to my Ubuntu 18.04.5 computer, using qjackctl 0.4.5, qsynth 0.5.0 and vmpk 0.4.0. I connect the microKEY2 to the qsynth and the VMPK. The patchbay is set up with these connections: Output Input PulseAudio JACK Sink and qsynth connect to system a2j 2 connected to a2j 2 Midi Through and microKEY2 connected to a2midid I can hear the synthesized piano in my headphones and see the VMPK keys activate. So far, so good. I'm using Zoom 5.4.9. I tried to follow the instructions at https://www.reddit.com/r/linuxaudio/comments/gckoia/midi_to_zoom_skype_etc/. I used paprefs to add simultaneous output on all sound cards. In this configuration, when I start Zoom and go to Settings and Audio, I cannot hear the Test Speaker sound, but can still hear my piano. When I connect to a meeting, the other participant can't hear me or the piano, and I can't hear them. I don't know what's meant by "open pavucontrol and under playback make qsynth output to the null sink. Under recording make the videochat application use the monitor of the null sink." These seem to be instruction for JACK, not pavucontrol. I've seen references to Carla, but it doesn't seem to be in my Ubuntu repository, and doesn't seem to be created for Ubuntu 18.04. Can anyone give me an insight to what I'm doing wrong and how to correct it? My normal troubleshooting technique of just try every possible combination until something works fails at this task; there's just too many moving parts. Thanks so much for your advice and guidance. Let me know if there's a more appropriate place to ask this question. -Kevin