As far as i understand, Panel builder only support 'tally'. But how about having the button lightened in either situation (for the operator to visually know if remote call is sent BUS or Master AUDIO). Hi ok for me to create 2 buttons for each talkback i need to use. If you have many presets to choose from, you might want to continue to use the List feature from UTC for now. You can use the Panel Builder to change contents of titles but you can only select 'NextTitlePreset' or 'PreviousTitlePreset' or 'SelectTitlePreset' commands to change the preset text. Admittedly, it's not ideal for talkback situations. Or you can create a script to 'toggle' between Master and Talkback Bus. You can however have one button to select the talkback bus and another button to select back to the master bus.
Currently the Panel Builder does not support 'Button Down' and Button Up' commands like a midi controller would and thus does not allow for momentary actions within one button (except for PTZ commands).